3 8 COLIFORM BACTERIA AS INDICATOR ORGANISMS Laboratory tests for disease-producing bacteria, viruses, and protozoa are difficult to perform

Transcription

1 3 8 COLIFORM BACTERIA AS INDICATOR ORGANISMS Laboratory tests for disease-producing bacteria, viruses, and protozoa are difficult to perform Most utilities have neither qualified personnel nor laboratories equipped to monitor for pathogens Available methods for detection and identification of human pathogens do not produce credible data for making public health decisions For these reasons, microbiological quality of water is based on testing for nonpathogenic indicator organisms principally the coliform group

2 3 8 COLIFORM BACTERIA AS INDICATOR ORGANISMS Pathogenic bacteria, viruses, and protozoa causing human enteric diseases come from the same source. Fecal discharges of diseased persons Water contaminated by fecal pollution is identified as potentially dangerous by the presence of coliforms In a similar manner, coliforms can be used as an indicator of water quality for reuse of reclaimed water

3 3 8 COLIFORM BACTERIA AS INDICATOR ORGANISMS The term total coliforms in laboratory testing refers to all coliform bacteria from feces, soil, or other origin Fecal coliforms refers to coliform bacteria originating from human or warm-blooded animal feces Reliability of coliform bacteria in indicating the presence of pathogens in water depends on the persistence of the pathogens relative to coliforms Significance of coliform testing in pollution surveys depends on a knowledge of the watershed And the most probable source of the observed coliforms

4 3 9 TESTS FOR THE COLIFORM GROUP The coliform group consists of several genera of bacteria in the family Enterobacteriaceae Which includes Escherichia coli All aerobic & facultative anaerobic, non-spore-forming, Gram-stain negative rods that ferment lactose with gas production within 48 hr of incubation at 35 C Extensive laboratory apparatus is needed to conduct bacteriological tests For detailed information, refer to Standard Methods

5 Multiple-Tube Fermentation Technique This technique tests for both total & fecal coliforms. From feces, soil, or other origins (Figs. 3 8 & 3 9) The most reliable technique for enumerating total coliforms and thermotolerant fecal coliforms In wastewater and surface waters Common usage is to monitor treated wastewater for compliance with a coliform standard And survey flowing and impounded waters for compliance with a water-quality standard

6 Multiple-Tube Fermentation Technique Bacterial density in a water sample can be determined by serial dilutions in multiple tubes using fermentation The result is reported as the most probable number (MPN) based on tabulated probability tables Expressed as MPN Index/100 ml The MPN Index and confidence limits for various combinations of positive and negative multiple-tube fermentation results can be determined on Table 3 2

7 Serial Dilution in Multiple Tubes Tests for bacterial density by inoculating fermentation tubes with only one dilution can be used for waters with low bacterial counts Such as wastewater after tertiary treatment MPN Index and confidence limits for 10 fermentation tubes using 10-ml portions are listed in Table 3 3

8 Presence Absence Technique The presence absence (P-A) test can determine if coliform bacteria or E. coli are present in a sample Without indicating number of coliforms in a positive result This test is intended for use in routine monitoring of drinking water immediately after treatment And in the distribution system pipe network The test is based on the concept that the most contaminant level (MCL) for coliform bacteria is zero

9 Sampling and Testing for Different Waters Coliform tests are performed ASAP after collection. If processing cannot be started within an hour, samples are stored at a temperature less than 10 C immediately Community drinking water samples that must be sent by mail or bus to a laboratory can be placed in an ice pack for up to 30 hr prior to testing

10 Sampling and Testing for Different Waters The best faucet in a distribution system for collecting a sample is a clean, single, cold-water inside faucet Supplied directly from the service pipe to the main Avoid faucets where water passes through a softener, filter, tank, or cistern; leaking faucets; swivel faucets and those with screens; and outside hydrants and sill cocks

11 Sampling and Testing for Different Waters During collection, be careful not to touch, or allow any object to contact, the inside of the cap, inside of the bottle, or threaded neck of the bottle Do not set the cap down The person collecting the sample should wash his or her hands before opening the bottle The (P-A) technique is the test recommended by the EPA for monitoring the microbiological quality of drinking water

12 3 10 BIOCHEMICAL OXYGEN DEMAND Biochemical oxygen demand (BOD) is the most common parameter to define the strength of municipal or organic industrial wastewater (Figs & 3 11) Its widest application is in measuring waste loadings to treatment plants and in evaluating the efficiency of such treatment systems In addition, the BOD test is used to determine the relative oxygen requirements of treated effluents and polluted waters

13 3 10 BIOCHEMICAL OXYGEN DEMAND BOD is by definition the quantity of oxygen utilized by a mixed population of microorganisms in the aerobic oxidation at a temperature of 20 C (+/-1 C) in an air incubator or water bath

14 BOD of Industrial Wastewater Although difficult, these tests are common in evaluating manufacturing wastes to assess sewer use fees or treatment plant loadings (Figs to 3-15) Most organic wastes from food-processing industries and other sources that are susceptible to biological decomposition can be tested for BOD The industry s type & quantity of production, and specific operational conditions should be recorded For correlation with quantity and strength of wastewater

15 BOD of Industrial Wastewater Very few industrial wastewaters have sufficient biological populations to perform BOD testing Without providing an acclimated seed The ideal seed is a mixed culture of bacteria/protozoa adapted to decomposing the specific industrial wastewater organics With a low number of nitrifying bacteria Microorganisms for food-processing wastes and similar organics can be obtained from aged untreated domestic wastewater

16 3 11 BIOLOGICAL TREATMENT SYSTEMS Biological processing is the most efficient way of removing organic matter from municipal wastewaters. Wastewater contains the biological food, growth nutrients, and inoculum of microorganisms By careful control of wastewater flows, recirculation of settled microorganisms, oxygen supply, and other factors, desirable biological cultures are generated

17 3 11 BIOLOGICAL TREATMENT SYSTEMS An anaerobic digester is the most difficult treatment unit to start up Since the methane-forming bacteria, essential to digestion, are not abundant in raw wastewater

18 3 11 BIOLOGICAL TREATMENT SYSTEMS Enzymes are organic catalysts that perform biochemical reactions at temperatures and chemical conditions compatible with biological Most enzymes cannot be isolated from living organisms without impairing their functioning capability Enzyme additives sold to enhance biological treatment processes are ineffective

19 Factors Affecting Biological Growth The most important factors affecting biological growth are temperature, availability of nutrients, oxygen supply, ph, presence of toxins, and, in the case of photosynthetic plants, sunlight

20 Factors Affecting Biological Growth Bacteria are classified according to their optimum temperature range for growth Rate of biological activity generally doubles or halves for every 10 to 15 C temperature rise or decrease Within the range of 5 to 35 C (Fig. 3 16) Warm wastewater has substantial influences on treatment processes by increasing the rate of bacterial activity and rate of chemical reactions

21 Factors Affecting Biological Growth Adverse effects of warm wastewater are: Greater release of hydrogen sulfide from anaerobic wastewater Increasing corrosion and emission of odors. Reduction in the density of settled sludge Due to fermentation of organic matter in the sludge blanket Increase in the rate of nitrification of ammonia Resulting in greater oxygen demand Difficulty in dewatering unstabilized waste sludge for disposal

22 Factors Affecting Biological Growth Benefits of warm wastewater: Higher allowable design loadings for wastewater aeration Due to increased rate of biological activity Reduced retention time for wastewater effluent disinfection Due to increased rate of the oxidative reaction of chlorine Improved biological treatment and more rapid die-off of pathogenic microorganisms in stabilization ponds

23 Factors Affecting Biological Growth Municipal wastewaters commonly contain sufficient carbon, nitrogen, phosphorus, and trace nutrients to support the growth of a microbial culture Hydrogen ion concentration has a direct influence on biological treatment systems The general range of operation of aeration systems is between ph 6.5 and 8.5 Biological treatment is inhibited by toxic substances. Pretreatment by industries prior to discharging wastes to the city sewer is required

24 Population Dynamics In biological processing, naturally occurring biota are bacteria growing in mutual association with other microscopic plants and animals (Figs & 3 18) Three of the major factors in population dynamics: Competition for the same food Predator prey relationship Symbiotic association Symbiosis is the living together of organisms for mutual benefit such that the association produces more vigorous growth of both species

25 Population Dynamics Control of the microbial populations is essential for efficient aerobic treatment Excess microorganisms are wasted from the process to maintain balance between food supply & biological mass The balance is referred to as a food-to-microorganism ratio (F/M), normally expressed in units of pounds of BOD applied per day per pound of MLSS in the basin MLSS is the mixed liquor suspended solids

26 Population Dynamics Control of the microbial populations is essential for efficient aerobic treatment Excess microorganisms are wasted from the process to maintain balance between food supply & biological mass The balance is referred to as a food-to-microorganism ratio (F/M), normally expressed in units of pounds of BOD applied per day per pound of MLSS in the basin MLSS is the mixed liquor suspended solids

27 Population Dynamics Operation at a high F/M ratio results in: Incomplete metabolism of the organic matter Poor settling characteristics of the biological floc Poor BOD removal efficiency At a low F/M ratio, the mass of microorganisms are in a near-starvation condition, which results in: A high degree of organic matter removal Good settleability of the activated sludge Efficient BOD removal

28 3 12 BIOLOGICAL KINETICS Characteristic growth patterns for a single bacterial species in a batch culture occur when a sterile liquid substrate is inoculated with a small number of bacteria (Figs & 3 20)

29 3 12 BIOLOGICAL KINETICS In the exponential growth phase, increase in the number of viable cells and accumulation of biomass is limited only by the ability of the bacteria to reproduce The declining growth phase is the result of diminishing substrate, limiting bacterial growth Growth yield is the incremental increase in biomass resulting from metabolism of an incremental amount of substrate