Test Bank Ch1 Free Essays

Test Bank—Chapter One (Data Representation) Multiple Choice Questions 1. Which of the following Boolean operations produces the output 1 for the fewest number of input patterns? A. ANDB. We will write a custom essay sample on Test Bank Ch1 or any similar topic only for you Order Now ORC. XOR ANSWER: A 2. Which of the following best describes the NOR operation? A. An XOR followed by a NOTB. An OR followed by a NOT C. A NOT followed by a NOTC. An AND followed by a NOT ANSWER: B 3. Which of the following bit patterns cannot be expressed in hexadecimal notation? A. 11111111B. 1001C. 110011D. 100000000001 ANSWER: C 4. Which of the following is the binary representation of 4 5/8? A. 100. 11B. 10. 11C. 110. 101D. 100. 101 ANSWER: D 5. Which of the following bit patterns represents the value 5 in two’s complement notation? A. 00011010B. 11111011C. 00000101D. 11111011 ANSWER: C 6. Which of the following bit patterns represents the value -5 in two’s complement notation? A. 00011010 B. 11111011C. 00000101 D. 11111011 ANSWER: D 7. In which of the following addition problems (using two’s complement notation) does an overflow error occur? A. 0011 B. 0100 C. 1100 + 1010 + 0100 + 1100 ANSWER: B 8. Which of the following representations in two’s comp lement notation represents the largest value? A. 00000010B. 11111111C. 00000001D. 11111110 ANSWER: A 9. Which of the following bit patterns (represented in hexadecimal notation) represents a negative number in two’s complement notation? A. 7FB. 55C. A6D. 08 ANSWER: C 10. What value is represented by the bit pattern 01011100 when interpreted using floating-point format in which the most significant bit is the sign bit, the next three bits represent the exponent field in excess notation, and the last four bits represent the mantissa? A. -1 1/2 B. 1 1/2C. -3/8 D. 3/8 ANSWER: B 11. Which of the following values cannot be stored accurately using a floating-point format in which the most significant bit is the sign bit, the next three bits represent the exponent field in excess notation, and the last four bits represent the mantissa? A. 2 1/2B. 3/16C. 7D. 6 1/4 ANSWER: D 121. Which of the following bit-patterns represents the smallest value using the floating-point format in which the most significant bit is the sign bit, the next three bits represent the exponent field in excess notation, and the last four bits represent the mantissa? A. 01001000B. 1011000C. 00101000D. 01111000 ANSWER: C 13. Which of the following data storage systems provides the most efficient random access to individual data items? A. Main memoryB. Magnetic diskC. Optical CDs and DVDs ANSWER: A 14. Which of the following storage systems is best suited for storing and retrieving long strings of data that are processed in their sequential order? A. Main memoryB. Magnetic diskC. Optical CDs and DVDs ANSWER: C 15. Which of the following mass storage system does not require physical motion? A. Magnetic tapeB. Magnetic diskC. DVDsD. Flash drives ANSWER: D 16. Assuming that each of the following bit patterns originally had even parity, which one contains an error? A. 10110100B. 11000011C. 00011000 D. 10001001 ANSWER: D 17. How many errors per pattern could be corrected when using an error-correcting code in which any two code patterns differ by a Hamming distance of 8? A. 3B. 4C. 5D. 6 ANSWER: A 18. Which of the following is a possible LZW compression of the message â€Å"xyz xyz xyz†? A. 1234B. 1234545C. 232D. 12 ANSWER: B 19. How many different symbols can be encoded using Unicode? A. 256B. 4,096C. 65,536D. 1,046,476 ANSWER: C 20. Which of the following systems is least efficient when encoding numeric values? A. Two’s complement notationB. Excess notation C. ASCIID. Floating-point notation ANSWER: C 21. Which of the following is a means of encoding music? A. ASCIIB. MIDIC. JPEGD. GIF ANSWER: B Fill-in-the-blank/Short-answer Questions 1. A computer’s main memory consists of numerous memory cells, each of which contains ________ bits. Each memory cell is identified by a numeric value called the cell’s _________. ANSWER: eight, address 2. Represent the bit pattern 1011010010011111 in hexadecimal notation. ________ ANSWER: B49F 3. A7DF is the hexadecimal representation for what bit pattern? ____________ ANSWER: 1010 0111 1101 1111 4. How many different bit patterns can be formed if each must consist of exactly 6 bits? ____________ ANSWER: 64 5. Translate each of the following binary representations into its equivalent base ten representation. A. 1100__________ B. 10. 011__________ C. 0. 01 ___ _______ D. 10001__________ ANSWER: A. 12 B. 2 3/8 C. 1/4 D. 17 6. Rewrite each of the following values (represented in base ten notation) in binary notation. A. 7__________ B. 23__________ C. 2 1/4 __________ D. 5/8__________ ANSWER: A. 111 B. 10111 C. 10. 01 D. 0. 101 7. If the patterns 101. 11 and 1. 011 represent values in binary notation, what is the binary representation of their sum? ____________ ANSWER: 111. 001 8. Using a two’s complement notation system in which each value is represented by a pattern of six bits, represent the value 3. ____________ ANSWER: 000011 9. Using a two’s complement notation system in which each value is represented by a pattern of six bits, represent the value -3. ____________ ANSWER: 111101 10. What is the largest positive integer that can be represented in a two’s complement system in which each value is represented by eight bits? ____________ ANSWER: 127 (represented by 01111111) 11. In a two’s complement system, what value is represented by the pattern 11111111111111001? ____________ ANSWER: -7 12. When using two’s complement notation, what bit pattern represents the negation of 01101010? ____________ ANSWER: 10010110 13. What value is represented by each of the following patterns in excess notation? A. 10000 ____ B. 0110 ____ C. 1011 ____ ANSWER: A. 0, B. -2, C. 14. Using an 8-bit floating-point format in which the most significant bit is the sign bit, the next three bits represent the exponent field in excess notation, and the last four bits represent the mantissa, write the bit pattern that represents the value 1 3/4. (Use normalized form. ) ____________ ANSWER: 01011110 15. What is the largest value that can be represented in a floating-point sys tem in which each value is encoded by a byte whose most significant bit is the sign bit, the next three bits represent the exponent field in excess notation, and the last four bits represent the mantissa? ___________ ANSWER: 7 1/2 (represented as 01111111) 16. Which of the following addition problems cannot be solved accurately when using a floating-point system in which each value is encoded by a byte whose most significant bit is the sign bit, the next three bits represent the exponent field in excess notation, and the last four bits represent the mantissa? A. 2 1/2 + 1 3/8B. 3 1/2 + 4 1/2C. 7 + 3/4 ____________ ANSWER: A, B, and C 17. The following is an error-correcting code in which any two patterns differ by a Hamming distance of at least three. Symbol Representation A 000000 B 001111 C 010011 D 011100 E 100110 F 101001 G 110101 H 111010 Decode each of the following patterns 010011 ________101010 ________011000 ________101101 _______ ANSWER: C, H, D, F 18. How many errors in a single code pattern could be corrected when using an error-correcting code in which each code pattern is a Hamming distance of at least seven from any other code pattern? ____________ ANSWER: 3 19. The following is a message that was originally encoded so that each pattern had odd parity. Circle the patterns in which an error has definitely occurred. 0110101 11110000 10010010 00000000 11111111 00001000 00111101 ______________________________________ ANSWER: Second, fourth, fifth, and sixth 20. Data compression techniques apply various principles to reduce the size of data. One, called _______________________, avoids repeating long strings of the same data item. Another, called _______________________, encodes the difference between consecutive blocks of data rather than encoding eac h block in its entirety. Still another, called _________________________, uses short bit patterns to encode frequently occurring items and longer patterns to encode less frequent items. ANSWER: Run-length encoding, relative encoding, and frequency-dependent encoding. Vocabulary (Matching) Questions The following is a list of terms from the chapter along with descriptive phrases that can be used to produce questions (depending on the topics covered in your course) in which the students are ask to match phrases and terms. An example would be a question of the form, â€Å"In the blank next to each phrase, write the term from the following list that is best described by the phrase. † TermDescriptive Phrase bitBinary digit Boolean operationAND, OR, XOR, NOT addressA numeric value used to identify a memory cell exadecimal notationAn efficient way of representing bit patterns sectorA segment of a track in a mass storage system zoned-bit recordingA means of increasing the storage capacity of a magnetic disk system bufferA storage area used to hold data on a temporary basis, often as a step in transferring the data from one device to another ISOAn international organi zation for establishing standards ANSIA major standardization organization within the United States ASCIIA system developed by the American Standards Institute for encoding text. lip-flopA digital circuit capable of holding a single digit two’s complement notationA means of encoding whole numbers floating-point notationA means of encoding numeric values that may involve fractions truncationAn error that may occur when using floating-point notation pixelA small part of an image GIFA means of compressing an image file by restricting the number of colors available JPEGA means of compressing images by blurring the boundaries between different colors while maintaining all brightness information UnicodeA means of encoding text in which each symbol is represented by 16 bits LZWAn example of adaptive dictionary encoding MIDIA means of encoding music in terms of notes and instruments rather than actual audio Key fieldA part of a logical record in a file used to identify the record. VLSIA means of constructing complex circuitry in a very small space. General Format Questions 1. Describe how a computer can produce an incorrect answer when performing numerical computations even though it has not malfunctioned. ANSWER: Most students will probably refer to overflow and truncation errors. 2. Describe ho the concept of Hamming distance is used to produce an error-correcting code. ANSWER: By designing a code in which each pattern has a Hamming distance of n from any other pattern, patterns with fewer than n/2 errors can be corrected by replacing them with the code pattern that is closest. . a. What is the output of the circuit below? [pic] b. In general, how does the three-bit input pattern across the top of the diagram relate to the circuit’s output? ANSWER: a. 0 b. The output is 0 if the input parity is odd; the output is 1 if the input parity is even. 4. If the input and output bit patterns in the circuit below are interpreted as binary representations of numeric values, what operation does the circuit perform? [pic] ANSWER: T he circuit subtracts one (except for the case of the input being 000). . Explain why such terms as kilobyte, megabyte, and gigabyte have acquired double meanings. ANSWER: The prefixes kilo, mega, and giga are used traditionally to refer to units measured in powers of ten. However, due to the early misuse of the prefix kilo in reference to units of the size 1024, these prefixes are now often used to refer to units that are powers of two—especially when referring to the capacity of main memories. 6. Convert the following addition problem into two’s complement notation using four bits per value), perform the addition, convert the answer back into base ten notation, and explain the results. 6 + 3 ANSWER: In two’s complement notation the problem is to add 0110 and 0011. The sum is 1001 which translates to -7. This answer is incorrect due to overflow. 7. Under what condition is each of the following data compression techniques most effective? a. Run-length encoding b. Relative encoding ANSWER: a. Compresses most when data consists of long strings of the same entry. b. Compresses most when each block of data differs little from the previous block. 8. What is frequency-dependent encoding? ANSWER: Frequency-dependent encoding is an encoding system that uses short bit patterns to represent data items that occur most often and longer patterns to represent less frequently occurring items. The result is that entire blocks of data can be represented in less space than would be required if each data item were represented by the same size bit pattern. 9. Construct the entire two’s complement scale in which each value is represented by three bits. ANSWER: 3 011 2 010 1 001 0 000 -1 111 -2 110 -3 101 -4 100 10. To what does the term â€Å"normalized form† refer in the context of floating-point notation? ANSWER: Normalized form refers to a standard for positioning the bit pattern within the mantissa field. Many values can be represented in floating-point notation by different bit patterns, only one of which is in normalized form. Hence, restricting representations to normalized form assures that each value is represented by a unique pattern. 11. Explain why the final version of the dictionary need not be transmitted with a message encoded using LZW compression. ANSWER: The dictionary can be constructed during decompression in the same way it was constructed during compression. 12. Among the Boolean operations AND, OR, EXCLUSIVE OR, and NOT, which is least like the others? Explain your answer. ANSWER: There is not really a right or wrong answer. The student’s explanation is the most important part. Most students will probably answer NOT because it has only one input whereas the others have two. 3. If a term paper consisted 42 pages, each containing 40 lines of 100 symbols each (counting each space as a symbol), was to be encoded using Unicode, how many bytes of storage space would be required? ANSWER: 336,000 bytes (168,000 symbols times 2 bytes per symbol) 14. Explain why adding only a few characters to a text file may increase the file’s size by several hundred bytes and at other times may not increase the fil e’s size at all. ANSWER: File space is allocated in terms of physical records, each of which is several hundred bytes in size. Thus, the size of a file grows by physical record units rather than by byte size units. 15. In a two’s complement system, what value can be added to any other value without causing an overflow? How many values in the system have this property? Explain your answer. ANSWER: Adding the value 0 to any other value will not produce an overflow. However, if m is the largest positive integer that can be represented in the system, then any value in the range 1 to m will produce an overflow when added to m, and any value in the range -1 to -( m + 1) will produce an overflow when added to -( m + 1). How to cite Test Bank Ch1, Papers

Who Brought Bernadine Healy Down Essay Example

Who Brought Bernadine Healy Down? Paper Considering the fact that Healy succeeded another woman, Elizabeth Dole, as president of the Red Cross, it is highly unlikely that her difficulties with the board were solely because she was a woman. But, according to David McLaughlin, now chairman of the board, both Dole, the first woman president since founder Clara Barton and Healy were â€Å"fighting a culture, a culture that had grown up over a long period of time.† (Sontag, 2003, p. 34) It is easy to assume that the â€Å"culture† they were fighting was a male dominated one. Although Sontag’s article mentions the differences between Healy and Dole (i.e. that Dole had a more human touch) it is probable that the real reason for her problems is that the board had overextended its reach in the period between Dole’s departure and Healy’s arrival, and regarded Healy as the instrument to reign them in. We will write a custom essay sample on Who Brought Bernadine Healy Down? specifically for you for only $16.38 $13.9/page Order now We will write a custom essay sample on Who Brought Bernadine Healy Down? specifically for you FOR ONLY $16.38 $13.9/page Hire Writer We will write a custom essay sample on Who Brought Bernadine Healy Down? specifically for you FOR ONLY $16.38 $13.9/page Hire Writer Question 2. Healy’s method of leadership most closely follows the A1 model where the leader takes known information and then decides alone. (Vroom, n.d.)This can be seen in at least four major decisions mentioned in the article. First, Healy was held responsible for the firing of the two women who ran the Disaster Operations Center when their response to the crises at the Pentagon and in Pennsylvania on September 11 was sorely wanting. (Sontag, 2003, p. 34) Second, she summarily suspended the director of the Hudson County Chapter of the Red Cross and his bookkeeper without pay after embezzlement of funds was suspected. Although she turned out to be right, the board thought that she had handled the matter poorly. (Sontag, 2003, p. 35) Third, Healy took measures to assure the safety of their blood supply by deciding to hire several high-profile executives to oversee the process. (Sontag, 2003, p. 37) And fourth, Healy declared on her own initiative that the September 11th tragedy was in a class of its own, therefore necessitating a separate fund called the Liberty Fund for disaster relief. (Sontag, 2003, p. 38) Question 3. Although the Red Cross is a non-profit organization with a grass-roots, humanitarian face, in order for it to be effective it must be run as efficiently as a for-profit organization. Without structure and accountability the Red Cross cannot be expected to have the necessary funds and resources ready or to provide disaster relief when in an efficient manner on an immediate basis. The embezzlement of funds in New Jersey confirmed this. Question 4. McLaughlin’s statement about Healy’s loss of capital with the board means that every decision she made that did not sit well with the members of the board reduced the confidence of the board in her management of the Red Cross. The board may have been willing to overlook small or immaterial decisions but the fact that there were so many major autonomous decisions made by this take-charge woman depleted their confidence in her judgment to the point where she could not rebuild their trust. Remember that without any capital (confidence), one can earn no interest or profit (trust). References Sontag, Deborah. (2001, December 23). Who Brought Bernadine Healy Down? New York   Ã‚  Ã‚  Ã‚  Ã‚   Times Magazine, 32 – 40, 52. Vroom and Yetton’s Normative Model. (n.d.). ChangingMInds.org. Retrieved November   Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚   23, 2008, from http://changingminds.org/disciplines/leadership/theories/vroom_yetton.htm.

Mandarin Chinese Names of North American Cities

Mandarin Chinese Names of North American Cities Mandarin Chinese has a relatively limited stock of phonetics compared with other languages. When it comes to translating Western geographical names into Chinese characters, a close phonetic match is attempted. Consideration must also be given to the meaning of the chosen Chinese characters. Most geographical names are chosen as phonetic approximations of the Western names, but a few place names are descriptive. San Francisco, for example, is Jià ¹ JÄ «n ShÄ n, which translates as â€Å"Old Gold Mountain,† reminding us of the California gold rush. Most Mandarin Chinese geographical names sound strange to Western ears. This is because there is usually not an exact phonetic equivalent to the sounds of the English names. North American Cities Click on the links to hear the audio. English Name Chinese Characters Pinyin New York ç ´ Ã§ ´â€ž niÇ” yuÄ“ Boston æ ³ ¢Ã¥ £ «Ã©  â€œ bÃ…  shà ¬ dà ¹n Montreal è’™ç‰ ¹Ã¥ ©  mà ©ng tà ¨ là ³u Vancouver æ º «Ã¥â€œ ¥Ã¨  ¯ wÄ“n gÄ“ hu Toronto Ã¥ ¤Å¡Ã¥â‚¬ «Ã¥ ¤Å¡ duÃ…  là ºn duÃ…  Los Angeles æ ´â€ºÃ¦ â€°Ã§ £ ¯ luà ² shÄ n jÄ « San Francisco 舊金å ± ± jià ¹ jÄ «n shÄ n Chicago èŠ Ã¥Å   Ã¥â€œ ¥ zhÄ « jiÄ  gÄ“ Seattle è ¥ ¿Ã©â€ºâ€¦Ã¥Å"â€" xÄ « yÇŽ tà º Miami é‚ Ã©Ëœ ¿Ã¥ ¯â€  mi Ä  mà ¬ Houston ä ¼â€˜Ã¦â€" ¯Ã©  â€œ xiÃ… « sÄ « dà ¹n Portland æ ³ ¢Ã§â€° ¹Ã¨Ëœ ­ bÃ…  tà ¨ ln Washington è  ¯Ã§â€ºâ€ºÃ©  â€œ hu shà ¨ng dà ¹n New Orleans ç ´ Ã¥ ¥ §Ã¨â€° ¯ niÇ” o ling Philadelphia è ² »Ã¥Å¸Å½ fà ¨i chà ©ng Detroit Ã¥ ºâ€¢Ã§â€° ¹Ã¥ ¾â€¹ dÇ  tà ¨ lÇÅ" Dallas é â€Ã¦â€¹â€°Ã¦â€" ¯ d lÄ  sÄ « Atlanta ä ºÅ¾Ã§â€° ¹Ã¨Ëœ ­Ã¥ ¤ § y tà ¨ ln d San Diego è â€"Ã¥Å" °Ã§â€°â„¢Ã¥â€œ ¥ shà ¨ng dià © y gÄ“ Las Vegas 拉æâ€" ¯Ã§ ¶ ­Ã¥Å   Ã¦â€" ¯ lÄ  sÄ « wà ©i jiÄ  sÄ «

The Best Resources for Landing Your Retail Job

The Best Resources for Landing Your Retail Job If you’ve worked in retail before, you know that it’s not a job for the faint of heart. It can mean long hours of doing physical tasks, keeping a smile on your face when you’d rather be rolling your eyes, and- perhaps the most daunting piece of all- dealing with the public. If you haven’t worked in retail before, spoiler alert: it’s not going to be sunshine and roses every day. But if you have great customer service skills, need flexible hours, or want to gain experience as you work toward other goals, it can be a great fit for the short- or long-term. If you’re up to this challenge, we’ve got what you need to get started- or get to the next level. Step 1: Revamp Your ResumeIf you’re familiar with how we roll here at The Job Network, this one should not come as a surprise. A badass resume is the starting point for every job search in every field. Even if you’re referred for the job by someone you know, you still need to m ake a great first impression on anyone who hasn’t met you before, at a minimum. And your resume gives your friend some quick talking points that act as ammo when they’re advocating for you to get the gig. An updated resume is essential.How to Write a Perfect Retail Resume (Examples Included)How to Write a Perfect Cashier Resume (Examples Included)How to Write a Perfect Sales Associate Resume (Examples Included)How to Create a Perfect Retail ResumeThe Ultimate 6 Step Guide to Resume WritingResume Headlines to Use for Different Jobs6 Ways to Make ATS Work in Your FavorResume Format Guide: What Your Resume Should Look Like in 2017Top Resume Trends for 20176 Job Skills You Need to Be a Sales AssociateDownload Resume TemplatesIt’s best to revamp your resume before you even start thinking about applying for jobs. This can keep you from making easy mistakes due to rushing, and lets you get a good baseline resume that you can use to adapt easily for each job application or opportunity.Step 2: Target Your Job SearchIf you want to start with a general geographic area or any type of stores, then a general search can be a great first step. It’s important to know what you’re looking for, to help focus your job hunt. If you need a starting point, we have plenty of recommendations that can help you find the type of retail job that works best for you.10 Summer Jobs- and How to Get ThemBest Jobs in Retail- and How to Get ThemTop 5 Less Crowded Sites to Look For Retail Jobs10 of the Best Jobs in Retail NationwideA Comprehensive Guide to Getting Different Types of Retail Jobs7 Places to Look for Part-Time JobsStep 3: Get Ready for the InterviewIn the retail world, hiring can move fast, so to paraphrase Ferris Bueller, if you aren’t ready for it, it can pass you by. You can start prepping for interviews before you even have one on the books.5 Questions to Expect in a Retail InterviewThe Most Popular Macy’s Interview QuestionsHow to Survive Your Upcoming Panel InterviewHow to Look Like a Star in Any Job InterviewHow to Answer the â€Å"What’s Your Biggest Weakness?† Question10 Things You Should Not Say in an Interview7 Real Life Interview Mistakes You Can Learn FromImpress Your Interviewer in 5 Simple Steps to Get the JobStep 4: Think About Your Career GoalsA job in retail might be your calling, or it might be just one step along your long career path. Whatever the case may be, it’s important to think about how you can a) be prepared for this job, and b) make it work for your future.How to Move Up the Retail Career Ladder Without CollegeWhat You Need to Know to Succeed in the Retail Industry5 Great Career Paths You Can Take If You’re Working in RetailWhether it’s your dream job or your right-now job, getting a job in retail is a challenge to be faced with as much ammo as you have at your disposal. If you’re ready to get started in this field, good luck!

Augmentation of our natural abilities using technology Case Study

Augmentation of our natural abilities using technology - Case Study Example Jumping stilts were invented and patented by a German aerospace engineer known as Alexander Boeck, who came up with the invention after studying the movement and structure of the kangaroo. The question that we seek to answer is whether jumping stilts are the ideal bionics that will enhance the historical wish of man to lift him from the ground, to some it can be said to be a craze but the possibilities that this bionic holds, is deemed to be phenomenon . It should be noted that stilts have been in existence in various human societies for a couple of centuries including African, Aboriginal and Chinese societies. The good thing is that using technology current generation can use jumping stilts in a way their ancestors never deemed possible. The feats that can be achieved using jumping stilts are taunted to be unimaginable in various aspects of human life. The device uses the concept of enhancing mans Achilles tendons by reducing friction at the knee joint and promoting balance on the f eet. Jumping stilts open possibilities of what augmented human beings can be able to do including jumping and running. The many uses at the moment of jumping stilts are not limited to the following artistic expression, form of exercise which tones the whole body unlike conventional exercise routines and also is a sport to enthusiasts. The fields that will greatly benefit from stilts are athletics and exercise; this is because it takes training of performers to the next level. It is deemed to be the next big thing in the fitness industry because it provides full body workout once, something not possible with traditional exercise regimes. Robotics which is a craze in the science community will benefit from this device because they can enhance human legs to make them look like robotic animals. The phenomenal recognition of this wearable human enhancement has lead to increased recognition in the international arena such that it was used during the closing ceremony of the 2008 Beijing Ol ympic in China. Man is essentially using the feat which can be achieved by the fastest animals on the planet such as ostriches and kangaroos. The main obstacle facing its distribution is perception and also coming up with a common name. This laboratory report will work on the above considerations to prove the hypothesis and assumptions which are stated below. The adrenalin of putting the stilts on, and running or jumping with them is reported by users to be like no other, which enhances locomotion greatly. The hypothesis and assumptions will rely on the observations and experiment to persuade the scientific community that they are true. 1) Hypothesis. This is the main wearable enhancement that enables people to jump very high and run very fast, compared to when they do that on foot. Theses should however not be confused with the prosthetics worn by disabled people who participate in the Paralympics. The questions which we seek to answer is whether these bionic enhancement can enable man to get off the ground and be the fastest mammal on the earth and whether this would open possibilities for man in various fields which otherwise not be possible if we only used our natural limbs without augmentation. Already such possibilities are being tested to be used by the military, an aspect who knows which could change warfare. The ultimate aim is for this argument to be proved to be a theory by other experimenters. This

Agriculture's importance economic progress Essay

Agriculture's importance economic progress - Essay Example Agriculture which is predominantly the base of systems of economy in most of the under developed countries is the primary occupation of rural people in those countries. It is primary because it supplies basic necessities of human life, provides basic inputs for industries and, in addition to these, purveys goods for exports and other purposes. â€Å". . . the rise in agricultural production . . . makes important contributions to general economic development and that, within considerable limits at least, it is one of the preconditions which must be established before a take off into self sustained economic growth becomes possible† (Nicholls, 1970). Earlier development economists like Arthur Lewis (1954), Hirschman (1958) and Fei and Ranis (1961) have identified and analyzed how agriculture contributes to the overall economic growth of a country (Higgins, 1982). They highlighted that the ‘unlimited labor supply’ in the agricultural sector of an underdeveloped countr y can be transformed to industrial sector and the ability of agriculture to transfer its abundant resources to other sectors actually lead the economic growth of any country. Contribution of agriculture in an economy is judged by the value of the total quantity of output in the Net National Product (NNP). A ratio between the output of agricultural sector and the output of non-agricultural sector or the proportion of the former in the NNP furnishes reasonable evidence not only of the nature of economy but also its stage of development. Simon Kuznets (1961) observes that â€Å"an increase in the net output of the agriculture is, in and of itself, sum of the increases in the net products of the several sectors† (61). So long as the rate of growth of the non-agricultural sector is higher than that of the agricultural sector, the proportional contribution of agriculture in the total product will decline. His model for assessing the product contributions to the NNP quite explicit a nd it is delineated as follows: dP=A.a+O.o Where, A= Product of Agriculture; O = Product of all other sectors; P= Total Proudct =(A+O); a=rate of growth of A ; o=Rate of Growth of O; d= change. The increment in the total product is the aggregate of products of sectarian outputs as multiplied by their respective rates of growth. Role of Agriculture in Economic Development- Traditional approach The traditional and earlier approaches proposed by development economists like Lewis, Fie and Ranis highlighted the important roles of agriculture sector in the economic development of any country (Vogel, 1994). A fast track development of this sector is crucial for other sectors as well. Only a strong and efficient agricultural sector can feed the growing population of a country, provide employment, play vital role in the foreign trade and earning of foreign exchange and give a strong base to the industries. Because of these multifaceted functions of agriculture, it has got a multiplier effect on any country’s socio-economic and industrial scenario. Thus according to the traditional analysis the role of the agricultural sector is confined to the source of food, source of livelihood, role in foreign trade, capital/savings transfers and its role in industrial development (Stringer, 2001). Source of Lively hood Most of the developing countries depend on agriculture and allied activities for their livelihood. Agriculture provides immense employment opportunities to the masses and this assumes much significance when the growing working force does not come out of the yoke. The figure may be varied from 10 percent to 60 percent in the contemporary scenario generally prevailing in the developing and underdeveloped countries across the globe (Stringer, 2001). Importance in the context of food security The character and content of a country’s economic structure alongside the potential for its further growth and development are largely dependent not only upon the quan tity but also upon the type of its output generated and distributed in the economy (FAO, 2001). For example, an

Evaluating The Waste Water Treatment Processes Environmental Sciences Essay

Evaluating The Waste Water Treatment Processes Environmental Sciences Essay Domestic wastewater treatment or sewage treatment, is the process of removing contaminants from wastewater and household sewage, both runoff (effluents) and domestic. It includes physical, chemical, and biological processes to remove physical, chemical and biological contaminants. Its objective is to produce an environmentally-safe fluid waste stream (or treated effluent) and a solid waste (or treated sludge) suitable for disposal or reuse (usually as farm fertilizer). Using advanced technology it is now possible to re-use sewage effluent for drinking water, although Singapore is the only country to implement such technology on a production scale in its production of NEWater. 1.2 ORIGIN OF WASTE WATER Sewage is created by residential, institutional, and commercial and industrial establishments and includes household waste liquid from toilets, baths, showers, kitchens, sinks and so forth that is disposed of via sewers. In many areas, sewage also includes liquid waste from industry and commerce. The separation and draining of household waste into greywater and blackwater is becoming more common in the developed world, with greywater being permitted to be used for watering plants or recycled for flushing toilets. Sewage may include stormwater runoff. Sewerage systems capable of handling stormwater are known as combined systems. Combined sewer systems are usually avoided now because precipitation causes widely varying flows reducing sewage treatment plant efficiency. Combined sewers require much larger, more expensive, treatment facilities than sanitary sewers. Heavy storm runoff may overwhelm the sewage treatment system, causing a spill or overflow. Sanitary sewers are typically much smaller than combined sewers, and they are not designed to transport stormwater. Backups of raw sewage can occur if excessive Infiltration/Inflow is allowed into a sanitary sewer system. Modern sewered developments tend to be provided with separate storm drain systems for rainwater. As rainfall travels over roofs and the ground, it may pick up various contaminants including soil particles and other sediment, heavy metals, organic compounds, animal waste, and oil and grease. (See urban runoff.) Some jurisdictions require stormwater to receive some level of treatment before being discharged directly into waterways. Examples of treatment processes used for stormwater include retention basins, wetlands, buried vaults with various kinds of media filters, and vortex separators (to remove coarse solids). CHAPTER TWO 2.1 OVERVIEW OF WASTE WATER TREATMENT PROCESSES Sewage can be treated close to where it is created, a decentralised system, (in septic tanks, biofilters or aerobic treatment systems), or be collected and transported via a network of pipes and pump stations to a municipal treatment plant, a centralised system, (see sewerage and pipes and infrastructure). Sewage collection and treatment is typically subject to local, state and federal regulations and standards. Industrial sources of wastewater often require specialized treatment processes as shown in the diagram below: Process Flow Diagram for a typical treatment plant via Subsurface Flow Constructed Wetlands (SFCW) Sewage treatment generally involves three stages, called primary, secondary and tertiary treatment. Primary treatment consists of temporarily holding the sewage in a quiescent basin where heavy solids can settle to the bottom while oil, grease and lighter solids float to the surface. The settled and floating materials are removed and the remaining liquid may be discharged or subjected to secondary treatment. Secondary treatment removes dissolved and suspended biological matter. Secondary treatment is typically performed by indigenous, water-borne micro-organisms in a managed habitat. Secondary treatment may require a separation process to remove the micro-organisms from the treated water prior to discharge or tertiary treatment. Tertiary treatment is sometimes defined as anything more than primary and secondary treatment in order to allow rejection into a highly sensitive or fragile ecosystem (estuaries, low-flow rivers, coral reefs etc.). Treated water is sometimes disinfected chemically or physically (for example, by lagoons and microfiltration) prior to discharge into a stream, river, bay, lagoon or wetland, or it can be used for the irrigation of a golf course, green way or park. If it is sufficiently clean, it can also be used for groundwater recharge or agricultural purposes. 2.2 PRE-TREATMENT Pre-treatment removes materials that can be easily collected from the raw waste water before they damage or clog the pumps and skimmers of primary treatment clarifiers (trash, tree limbs, leaves, etc.). SCREENING The influent sewage water is screened to remove all large objects like cans, rags, sticks, plastic packets etc. carried in the sewage stream. This is most commonly done with an automated mechanically raked bar screen in modern plants serving large populations, whilst in smaller or less modern plants a manually cleaned screen may be used. The raking action of a mechanical bar screen is typically paced according to the accumulation on the bar screens and/or flow rate. The solids are collected and later disposed in a landfill or incinerated. Bar screens or mesh screens of varying sizes may be used to optimize solids removal. If gross solids are not removed they become entrained in pipes and moving parts of the treatment plant and can cause substantial damage and inefficiency in the process. GRIT REMOVAL Pre-treatment may include a sand or grit channel or chamber where the velocity of the incoming wastewater is adjusted to allow the settlement of sand, grit, stones, and broken glass. These particles are removed because they may damage pumps and other equipment. For small sanitary sewer systems, the grit chambers may not be necessary, but grit removal is desirable at larger plants. FAT AND GREASE REMOVAL In some larger plants, fat and grease is removed by passing the sewage through a small tank where skimmers collect the fat floating on the surface. Air blowers in the base of the tank may also be used to help recover the fat as a froth. In most plants however, fat and grease removal takes place in the primary settlement tank using mechanical surface skimmers. 2.3 PRIMARY TREATMENT In the primary sedimentation stage, sewage flows through large tanks, commonly called primary clarifiers or primary sedimentation tanks. The tanks are used to settle sludge while grease and oils rise to the surface and are skimmed off. Primary settling tanks are usually equipped with mechanically driven scrapers that continually drive the collected sludge towards a hopper in the base of the tank where it is pumped to sludge treatment facilities. Grease and oil from the floating material can sometimes be recovered for saponification. The dimensions of the tank should be designed to effect removal of a high percentage of the floatables and sludge. A typical sedimentation tank may remove from 60 to 65 percent of suspended solids, and from 30 to 35 percent of biochemical oxygen demand (BOD) from the sewage. 2.4 SECONDARY TREATMENT Secondary treatment is designed to substantially degrade the biological content of the sewage which are derived from human waste, food waste, soaps and detergent. The majority of municipal plants treat the settled sewage liquor using aerobic biological processes. To be effective, the biota require both oxygen and food to live. The bacteria and protozoa consume biodegradable soluble organic contaminants (e.g. sugars, fats, organic short-chain carbon molecules, etc.) and bind much of the less soluble fractions into floc. Secondary treatment systems are classified as fixed-film or suspended-growth systems. Fixed-film or attached growth systems include trickling filters and rotating biological contactors, where the biomass grows on media and the sewage passes over its surface. Suspended-growth systems include activated sludge, where the biomass is mixed with the sewage and can be operated in a smaller space than fixed-film systems that treat the same amount of water. However, fixed-film systems are more able to cope with drastic changes in the amount of biological material and can provide higher removal rates for organic material and suspended solids than suspended growth systems.[6]:11-13 Roughing filters are intended to treat particularly strong or variable organic loads, typically industrial, to allow them to then be treated by conventional secondary treatment processes. Characteristics include filters filled with media to which wastewater is applied. They are designed to allow high hydraulic loading and a high level of aeration. On larger installations, air is forced through the media using blowers. The resultant wastewater is usually within the normal range for conventional treatment processes. A generalized, schematic diagram of an activated sludge process. A filter removes a small percentage of the suspended organic matter, while the majority of the organic matter undergoes a change of character, only due to the biological oxidation and nitrification taking place in the filter. With this aerobic oxidation and nitrification, the organic solids are converted into coagulated suspended mass, which is heavier and bulkier, and can settle to the bottom of a tank. The effluent of the filter is therefore passed through a sedimentation tank, called a secondary clarifier, secondary settling tank or humus tank. ACTIVATED SLUDGE In general, activated sludge plants encompass a variety of mechanisms and processes that use dissolved oxygen to promote the growth of biological floc that substantially removes organic material. The process traps particulate material and can, under ideal conditions, convert ammonia to nitrite and nitrate and ultimately to nitrogen gas. SURFACE-AERATED BASINS (LAGOONS) Many small municipal sewage systems in the United States (1 million gal./day or less) use aerated lagoons. Most biological oxidation processes for treating industrial wastewaters have in common the use of oxygen (or air) and microbial action. Surface-aerated basins achieve 80 to 90 percent removal of BOD with retention times of 1 to 10 days. The basins may range in depth from 1.5 to 5.0 metres and use motor-driven aerators floating on the surface of the wastewater. In an aerated basin system, the aerators provide two functions: they transfer air into the basins required by the biological oxidation reactions, and they provide the mixing required for dispersing the air and for contacting the reactants (that is, oxygen, wastewater and microbes). Typically, the floating surface aerators are rated to deliver the amount of air equivalent to 1.8 to 2.7  kg O2/kW ·h. However, they do not provide as good mixing as is normally achieved in activated sludge systems and therefore aerated basins do not achieve the same performance level as activated sludge units. Biological oxidation processes are sensitive to temperature and, between 0  °C and 40  °C, the rate of biological reactions increase with temperature. Most surface aerated vessels operate at between 4  °C and 32  °C. CONSTRUCTED WETLANDS Constructed wetlands (can either be surface flow or subsurface flow, horizontal or vertical flow), include engineered reedbeds and belong to the family of phytorestoration and ecotechnologies; they provide a high degree of biological improvement and depending on design, act as a primary, secondary and sometimes tertiary treatment, also see phytoremediation. One example is a small reedbed used to clean the drainage from the elephants enclosure at Chester Zoo in England; numerous CWs are used to recycle the water of the city of Honfleur in France and numerous other towns in Europe, the US, Asia and Australia. They are known to be highly productive systems as they copy natural wetlands, called the Kidneys of the earth for their fundamental recycling capacity of the hydrological cycle in the biosphere. Robust and reliable, their treatment capacities improve as time go by, at the opposite of conventional treatment plants whose machinery age with time. They are being increasingly used, alt hough adequate and experienced design are more fundamental than for other systems and space limitation may impede their use. FILTER BEDS (OXIDIZING BEDS) In older plants and those receiving variable loadings, trickling filter beds are used where the settled sewage liquor is spread onto the surface of a bed made up of coke (carbonized coal), limestone chips or specially fabricated plastic media. Such media must have large surface areas to support the biofilms that form. The liquor is typically distributed through perforated spray arms. The distributed liquor trickles through the bed and is collected in drains at the base. These drains also provide a source of air which percolates up through the bed, keeping it aerobic. Biological films of bacteria, protozoa and fungi form on the medias surfaces and eat or otherwise reduce the organic content. This biofilm is often grazed by insect larvae, snails, and worms which help maintain an optimal thickness. Overloading of beds increases the thickness of the film leading to clogging of the filter media and ponding on the surface. SOIL BIO-TECHNOLOGY A new process called Soil Bio-Technology (SBT) developed at IIT Bombay has shown tremendous improvements in process efficiency enabling total water reuse, due to extremely low operating power requirements of less than 50 joules per kg of treated water. Typically SBT systems can achieve chemical oxygen demand (COD) levels less than 10  mg/L from sewage input of COD 400  mg/L. SBT plants exhibit high reductions in COD values and bacterial counts as a result of the very high microbial densities available in the media. Unlike conventional treatment plants, SBT plants produce insignificant amounts of sludge, precluding the need for sludge disposal areas that are required by other technologies. BIOLOGICAL AERATED FILTERS Biological Aerated (or Anoxic) Filter (BAF) or Biofilters combine filtration with biological carbon reduction, nitrification or denitrification. BAF usually includes a reactor filled with a filter media. The media is either in suspension or supported by a gravel layer at the foot of the filter. The dual purpose of this media is to support highly active biomass that is attached to it and to filter suspended solids. Carbon reduction and ammonia conversion occurs in aerobic mode and sometime achieved in a single reactor while nitrate conversion occurs in anoxic mode. BAF is operated either in upflow or downflow configuration depending on design specified by manufacturer. Schematic diagram of a typical rotating biological contactor (RBC). The treated effluent clarifier/settler is not included in the diagram. ROTATING BIOLOGICAL CONTACTORS Rotating biological contactors (RBCs) are mechanical secondary treatment systems, which are robust and capable of withstanding surges in organic load. RBCs were first installed in Germany in 1960 and have since been developed and refined into a reliable operating unit. The rotating disks support the growth of bacteria and micro-organisms present in the sewage, which break down and stabilise organic pollutants. To be successful, micro-organisms need both oxygen to live and food to grow. Oxygen is obtained from the atmosphere as the disks rotate. As the micro-organisms grow, they build up on the media until they are sloughed off due to shear forces provided by the rotating discs in the sewage. Effluent from the RBC is then passed through final clarifiers where the micro-organisms in suspension settle as a sludge. The sludge is withdrawn from the clarifier for further treatment. A functionally similar biological filtering system has become popular as part of home aquarium filtration and purification. The aquarium water is drawn up out of the tank and then cascaded over a freely spinning corrugated fiber-mesh wheel before passing through a media filter and back into the aquarium. The spinning mesh wheel develops a biofilm coating of microorganisms that feed on the suspended wastes in the aquarium water and are also exposed to the atmosphere as the wheel rotates. This is especially good at removing waste . MEMBRANE BIOREACTORS Membrane bioreactors (MBR) combine activated sludge treatment with a membrane liquid-solid separation process. The membrane component uses low pressure microfiltration or ultra filtration membranes and eliminates the need for clarification and tertiary filtration. The membranes are typically immersed in the aeration tank; however, some applications utilize a separate membrane tank. One of the key benefits of an MBR system is that it effectively overcomes the limitations associated with poor settling of sludge in conventional activated sludge (CAS) processes. The technology permits bioreactor operation with considerably higher mixed liquor suspended solids (MLSS) concentration than CAS systems, which are limited by sludge settling. The process is typically operated at MLSS in the range of 8,000-12,000  mg/L, while CAS are operated in the range of 2,000-3,000  mg/L. The elevated biomass concentration in the MBR process allows for very effective removal of both soluble and particula te biodegradable materials at higher loading rates. Thus increased sludge retention times, usually exceeding 15 days, ensure complete nitrification even in extremely cold weather. SECONDARY SEDIMENTATION The final step in the secondary treatment stage is to settle out the biological floc or filter material through a secondary clarifier and to produce sewage water containing low levels of organic material and suspended matter. TERTIARY TREATMENT The purpose of tertiary treatment is to provide a final treatment stage to raise the effluent quality before it is discharged to the receiving environment (sea, river, lake, ground, etc.). More than one tertiary treatment process may be used at any treatment plant. If disinfection is practiced, it is always the final process. It is also called effluent polishing. FILTRATION Sand filtration removes much of the residual suspended matter. Filtration over activated carbon, also called carbon adsorption, removes residual toxins. LAGOONING Lagooning provides settlement and further biological improvement through storage in large man-made ponds or lagoons. These lagoons are highly aerobic and colonization by native macrophytes, especially reeds, is often encouraged. Small filter feeding invertebrates such as Daphnia and species of Rotifera greatly assist in treatment by removing fine particulates. NUTRIENT REMOVAL Wastewater may contain high levels of the nutrients nitrogen and phosphorus. Excessive release to the environment can lead to a build up of nutrients, called eutrophication, which can in turn encourage the overgrowth of weeds, algae, and cyanobacteria (blue-green algae). This may cause an algal bloom, a rapid growth in the population of algae. The algae numbers are unsustainable and eventually most of them die. The decomposition of the algae by bacteria uses up so much of oxygen in the water that most or all of the animals die, which creates more organic matter for the bacteria to decompose. In addition to causing deoxygenation, some algal species produce toxins that contaminate drinking water supplies. Different treatment processes are required to remove nitrogen and phosphorus. NITROGEN REMOVAL The removal of nitrogen is effected through the biological oxidation of nitrogen from ammonia to nitrate (nitrification), followed by denitrification, the reduction of nitrate to nitrogen gas. Nitrogen gas is released to the atmosphere and thus removed from the water. Nitrification itself is a two-step aerobic process, each step facilitated by a different type of bacteria. The oxidation of ammonia (NH3) to nitrite (NO2à ¢Ã‹â€ Ã¢â‚¬â„¢) is most often facilitated by Nitrosomonas spp. (nitroso referring to the formation of a nitroso functional group). Nitrite oxidation to nitrate (NO3à ¢Ã‹â€ Ã¢â‚¬â„¢), though traditionally believed to be facilitated by Nitrobacter spp. (nitro referring the formation of a nitro functional group), is now known to be facilitated in the environment almost exclusively by Nitrospira spp. Denitrification requires anoxic conditions to encourage the appropriate biological communities to form. It is facilitated by a wide diversity of bacteria. Sand filters, lagooning and reed beds can all be used to reduce nitrogen, but the activated sludge process (if designed well) can do the job the most easily. Since denitrification is the reduction of nitrate to dinitrogen gas, an electron donor is needed. This can be, depending on the wastewater, organic matter (from faeces), sulfide, or an added donor like methanol. PHOSPHORUS REMOVAL Phosphorus removal is important as it is a limiting nutrient for algae growth in many fresh water systems. (For a description of the negative effects of algae, see Nutrient removal). It is also particularly important for water reuse systems where high phosphorus concentrations may lead to fouling of downstream equipment such as reverse osmosis. Phosphorus can be removed biologically in a process called enhanced biological phosphorus removal. In this process, specific bacteria, called polyphosphate accumulating organisms (PAOs), are selectively enriched and accumulate large quantities of phosphorus within their cells (up to 20 percent of their mass). When the biomass enriched in these bacteria is separated from the treated water, these biosolids have a high fertilizer value. Phosphorus removal can also be achieved by chemical precipitation, usually with salts of iron (e.g. ferric chloride), aluminum (e.g. alum), or lime. This may lead to excessive sludge production as hydroxides precipitates and the added chemicals can be expensive. Chemical phosphorus removal requires significantly smaller equipment footprint than biological removal, is easier to operate and is often more reliable than biological phosphorus removal  . Another method for phosphorus removal is to use granular laterite. Once removed, phosphorus, in the form of a phosphate-rich sludge, may be stored in a land fill or resold for use in fertilizer. DISINFECTION The purpose of disinfection in the treatment of waste water is to substantially reduce the number of microorganisms in the water to be discharged back into the environment. The effectiveness of disinfection depends on the quality of the water being treated (e.g., cloudiness, pH, etc.), the type of disinfection being used, the disinfectant dosage (concentration and time), and other environmental variables. Cloudy water will be treated less successfully, since solid matter can shield organisms, especially from ultraviolet light or if contact times are low. Generally, short contact times, low doses and high flows all militate against effective disinfection. Common methods of disinfection include ozone, chlorine, ultraviolet light, or sodium hypochlorite. Chloramine, which is used for drinking water, is not used in waste water treatment because of its persistence. Chlorination remains the most common form of waste water disinfection in North America due to its low cost and long-term history of effectiveness. One disadvantage is that chlorination of residual organic material can generate chlorinated-organic compounds that may be carcinogenic or harmful to the environment. Residual chlorine or chloramines may also be capable of chlorinating organic material in the natural aquatic environment. Further, because residual chlorine is toxic to aquatic species, the treated effluent must also be chemically dechlorinated, adding to the complexity and cost of treatment. Ultraviolet (UV) light can be used instead of chlorine, iodine, or other chemicals. Because no chemicals are used, the treated water has no adverse effect on organisms that later consume it, as may be the case with other methods. UV radiation causes damage to the genetic structure of bacteria, viruses, and other pathogens, making them incapable of reproduction. The key disadvantages of UV disinfection are the need for frequent lamp maintenance and replacement and the need for a highly treated effluent to ensure that the target microorganisms are not shielded from the UV radiation (i.e., any solids present in the treated effluent may protect microorganisms from the UV light). In the United Kingdom, UV light is becoming the most common means of disinfection because of the concerns about the impacts of chlorine in chlorinating residual organics in the wastewater and in chlorinating organics in the receiving water. Some sewage treatment systems in Canada and the US also use UV light for their effluent water disinfection. Ozone (O3) is generated by passing oxygen (O2) through a high voltage potential resulting in a third oxygen atom becoming attached and forming O3. Ozone is very unstable and reactive and oxidizes most organic material it comes in contact with, thereby destroying many pathogenic microorganisms. Ozone is considered to be safer than chlorine because, unlike chlorine which has to be stored on site (highly poisonous in the event of an accidental release), ozone is generated onsite as needed. Ozonation also produces fewer disinfection by-products than chlorination. A disadvantage of ozone disinfection is the high cost of the ozone generation equipment and the requirements for special operators. ODOUR CONTROL Odours emitted by sewage treatment are typically an indication of an anaerobic or septic condition. Early stages of processing will tend to produce smelly gases, with hydrogen sulfide being most common in generating complaints. Large process plants in urban areas will often treat the odours with carbon reactors, a contact media with bio-slimes, small doses of chlorine, or circulating fluids to biologically capture and metabolize the obnoxious gases. Other methods of odour control exist, including addition of iron salts, hydrogen peroxide, calcium nitrate, etc. to manage hydrogen sulfide levels. PACKAGE PLANTS AND BATCH REACTORS To use less space, treat difficult waste and intermittent flows, a number of designs of hybrid treatment plants have been produced. Such plants often combine at least two stages of the three main treatment stages into one combined stage. In the UK, where a large number of wastewater treatment plants serve small populations, package plants are a viable alternative to building a large structure for each process stage. In the US, package plants are typically used in rural areas, highway rest stops and trailer parks. One type of system that combines secondary treatment and settlement is the sequencing batch reactor (SBR). Typically, activated sludge is mixed with raw incoming sewage, and then mixed and aerated. The settled sludge is run off and re-aerated before a proportion is returned to the headworks. SBR plants are now being deployed in many parts of the world. The disadvantage of the SBR process is that it requires a precise control of timing, mixing and aeration. This precision is typically achieved with computer controls linked to sensors. Such a complex, fragile system is unsuited to places where controls may be unreliable, poorly maintained, or where the power supply may be intermittent. Extended aeration package plants use separate basins for aeration and settling, and are somewhat larger than SBR plants with reduced timing sensitivity. Package plants may be referred to as high charged or low charged. This refers to the way the biological load is processed. In high charged systems, the biological stage is presented with a high organic load and the combined floc and organic material is then oxygenated for a few hours before being charged again with a new load. In the low charged system the biological stage contains a low organic load and is combined with flocculate for longer times. SLUDGE TREATMENT AND DISPOSAL The sludges accumulated in a wastewater treatment process must be treated and disposed of in a safe and effective manner. The purpose of digestion is to reduce the amount of organic matter and the number of disease-causing microorganisms present in the solids. The most common treatment options include anaerobic digestion, aerobic digestion, and composting. Incineration is also used albeit to a much lesser degree. Sludge treatment depends on the amount of solids generated and other site-specific conditions. Composting is most often applied to small-scale plants with aerobic digestion for mid sized operations, and anaerobic digestion for the larger-scale operations. ANAEROBIC DIGESTION Anaerobic digestion is a bacterial process that is carried out in the absence of oxygen. The process can either be thermophilic digestion, in which sludge is fermented in tanks at a temperature of 55 °C, or mesophilic, at a temperature of around 36 °C. Though allowing shorter retention time (and thus smaller tanks), thermophilic digestion is more expensive in terms of energy consumption for heating the sludge. Anaerobic digestion is the most common (mesophilic) treatment of domestic sewage in septic tanks, which normally retain the sewage from one day to two days, reducing the BOD by about 35 to 40 percent. This reduction can be increased with a combination of anaerobic and aerobic treatment by installing Aerobic Treatment Units (ATUs) in the septic tank. One major feature of anaerobic digestion is the production of biogas (with the most useful component being methane), which can be used in generators for electricity production and/or in boilers for heating purposes. AEROBIC DIGESTION Aerobic digestion is a bacterial process occurring in the presence of oxygen. Under aerobic conditions, bacteria rapidly consume organic matter and convert it into carbon dioxide. The operating costs used to be characteristically much greater for aerobic digestion because of the energy used by the blowers, pumps and motors needed to add oxygen to the process. Aerobic digestion can also be achieved by using diffuser systems or jet aerators to oxidize the sludge. COMPOSTING Composting is also an aerobic process that involves mixing the sludge with sources of carbon such as sawdust, straw or wood chips. In the presence of oxygen, bacteria digest both the wastewater solids and the added carbon source and, in doing so, produce a large amount of heat. INCINERATION Incineration of sludge is less common because of air emissions concerns and the supplemental fuel (typically natural gases or fuel oil) required to burn the low calorific value sludge and vaporize residual water. Stepped multiple hearth incinerators with high residence time and fluidized bed incinerators are the most common systems used to combust wastewater sludge. Co-firing in municipal waste-to-energy plants is occasionally done, this option being less expensive assuming the facilities already exist for solid waste and there is no need for auxiliary fuel. CHAPTER THREE TERTIARY TREATMENT 3.1 SLUDGE DISPOSAL When a liquid sludge is produced, further treatment may be required to make it suitable for final disposal. Typically, sludges are thickened (dewatered) to reduce the volumes transported off-site for disposal. There is no process which completely eliminates the need to dispose of biosolids. There is, however, an additional step some cities are taking to superheat sludge and convert it into small pelletized granules that are high in nitrogen and other organic materials. In N