Water Quality:Wastewater Microbiology

By: Anna Mae CababarosMS EST-1

Wastewater is teaming with microbes. Many of which are necessary for the degradation and stabilization of organic matter and are beneficial. On the other hand, wastewater may also contain pathogenic or potentially pathogenic microorganisms, which pose a threat to public health.

Wastewater ConstituentsMajor classes:– Suspended solids (TSS, VSS, etc.)– Biodegradable organics (BOD, COD)– Pathogens (bacteria, viruses, protozoa, etc.)– Nutrients (N, P, etc.)– Priority pollutants– Organics that don’t biodegrade (refractory)– Heavy metals (Cd, Zn, Pb, Hg, Cu)– Ions (pH; contribute to TDS e.g. Ca2+, Na+,

SO4-2)– Temperature– Toxicity

Concentration

Parameter Strong(mg/L)

Medium(mg/L)

Weak(mg/L)

BOD5 400 220 110

COD 1000 500 250

Organic N 35 15 8

NH3-N 50 25 12

Total N 85 40 20

Total P 15 8 4

Total solids 1200 720 350

Suspended Solids

350 220 100

TABLE 1. Typical Characteristics of Domestic Wastewater

From Metcalf and Eddy Inc. (1991).

Many are human pathogens. Most occupy a role in the treatment process.

They are:– Bacteria – Viruses– Archaea – Algae– Fungi/yeast – Rotifers– Protozoa

Biological Constituents

Bacteria

Bacteria

Viruses

Viruses

Protozoa

Protozoa

Helminthes

Helminthes

HUMANS

HUMANS

Figure 1. Categories of organisms of public health significance.

BACTERIAL Pathogens: a)Some of these pathogens (e.g., Salmonella,

Shigella) are enteric bacteria. Others (e.g., Legionella, Mycobacterium avium, Aeromonas) are indigenous aquatic bacteria.

Pathogens and Parasites in Domestic Wastewater

Typhoid FeverSalmonella typhi– Diarrhea– Transmitted by contaminated food, direct

contact, and drinking water• Viruses - polio and hepatitis A– Maintaining of 0.6 μg/ml residual chlorine

assures elimination• Both diseases are transmitted from infected

individuals and in the developed world are associated with the breakdown of water treatment practices.

Legionella pneumophila a waterborne pathogen transmitted via

aerosols Found in water and soil but grows to high

numbers in warm waters (air conditioning cooling systems, hot pools)

• An intracellular parasite of alveolar macrophage and monocytes

Pontiac fever - mild headaches, sore throat, fever, that disappears after a few days

Pneumonia that follows flu-like symptoms in the elderly; 10% death

• Treated with erythromycin

VIRAL pathogens:b) Water and wastewater may become

contaminated by approximately 140 types of enteric viruses. These viruses enter into the human body orally, multiply in the gastrointestinal tract, and are excreted in large numbers in the feces of infected individuals.

They are responsible for a broad spectrum of diseases ranging from skin rash, fever, respiratory infections, and conjunctivitis to gastroenteritis and paralysis.

Viral Sources of Waterborne Disease

• Hepatitis A: readily transmitted via water; causes inflammation and necrosis of liver

• Norwalk-type viruses: cause acute gastroenteritis

• Rotavirus: causes acute gastroenteritis, especially in children

• Enteroviruses: many types can infect both the intestines and the upper respiratory tract

• Reoviruses: infect the intestines and upper respiratory tract (usually without disease symptoms)

PROTOZOAN parasites:c) These are released into aquatic environments as cysts or oocysts, which are quite resistant to environmental stress and to disinfection, and do not multiply outside their hosts.

Giardiasis and Cryptosporidiosis

• Giardia lamblia and Cryptosporidium parvum are protozoans

• G. lamblia cyst ingested and trophozoite develop, attach to intestine wall leading to diarrhea, foul smell, stomach cramps

• Transmission through water. 97% of all surface water carry cysts. Cysts are resistant to chlorine but proper water treatment removes them during flocculation and filtration

• Natural streams - transmission by wild animals• Diagnosis: microscopic observation or antigen

presence; treated with drugs

. Person-to-Person Transmission

. Waterborne Transmission

. Foodborne Transmission

. Airborne Transmission

. Vector-Borne Transmission

. Fomites

Mode of Transmission

Indicators and Detection

Indicator organisms indicate that fecal pollution has occurred and microbial pathogens might be present.

Total and fecal coliforms, and the enterococci -fecal streptococci are the indicator organisms currently used in the public health arena.

Bacterial-Indicator organisms

• COLIFORM GROUP–total coliforms –fecal coliforms –Escherichia coli

• STREPTOCOCCI–fecal streptococci (enterococci)

• SPORE FORMERS–Clostridium perfringens

Coliform Characteristics

• Total coliforms–Gram negative–Ferment lactose at 35° C–Ubiquitous in the

environment• Fecal coliforms–Ferment lactose at

44.5°C

–May be of fecal origin–Old recreational-use

criteria• Escherichia coli–Inhabits

gastrointestinal tract–Specific indicator of

fecal pollution

Other Fecal Indicators• Fecal streptococci (enterococci)–Gram-positive cocci–Grows at 41 °C

• Clostridium perfringens–Present in both human and animal wastes–Produces a stress-resistant spore–Indicates point sources, but poor indicator

ofnon-point pollution sources–Possible surrogate for resistant bacteria

Chemical Indicators of Water Quality

I. Fecal Sterols- coprostanol, coprosterol, cholesterol and coprostanone (correlation with fecal contamination)

II. Free Chlorine Residuals- good indicator for drinking water quality

III. Levels of EndotoxinsIV. Fluorescent Whitening Agents-

included in detergents and washing powders

Typical Water Quality Standards

• Drinking water–No coliform

contamination acceptable

• Public water supply water

–2000 fecal coliforms per 100 mL

• Recreational water–200 fecal coliforms

per 100 mL• Fish and wildlife

habitat– 5000 fecal

coliforms per 100 mL

• Shellfish–14 fecal coliforms

per 100 mL

Wastewater Disinfection

Disinfection is the destruction of microorganisms capable of causing diseases. Disinfection is an essential and final barrier against human exposure to disease-causing pathogenic microorganisms, including viruses, bacteria, and protozoan parasites.

Chlorination was initiated at the beginning of the twentieth century to provide an additional safeguard against pathogenic microorganisms.

Factors Influencing Disinfection

Types of Disinfectant Used

Type of Microorganisms present

Disinfectant Concentration and contact Time

Effect of pH

Temperature

Chemical and Physical Interference of Disinfection

Treatment methods based on chemical and biological processes are called unit processes.

Chemical unit processes include disinfection, adsorption, or precipitation.

Biological unit processes involve microbial activity, which is responsible for organic matter degradation and removal of nutrients (Metcalf and Eddy, 1991).

Wastewater Treatment

Objectives:1. Reduction of the organic content of

wastewater (i.e., reduction of BOD).2. Removal/reduction of trace organics that are recalcitrant to biodegradation and may be

toxic or carcinogenic.3. Removal/reduction of toxic metals.4. Removal/reduction of nutrients (N, P) to

reduce pollution of receiving surface waters or groundwater if the effluents are applied onto land.

5. Removal or inactivation of pathogenic microorganisms and parasites.

1. Preliminary treatment. The objective of this operation is to remove debris and coarse materials that may clog equipment in the plant.

2. Primary treatment. Treatment is brought about by physical processes (unit operations) such as screening and sedimentation.3. Secondary treatment. Biological (e.g., activated sludge, trickling filter, oxidation ponds) and chemical (e.g., disinfection) unit processes are used to treat wastewater. Nutrient removal also generally occurs during secondary treatment of wastewater.4. Tertiary or advanced treatment. Unit operations and chemical unit processes are used to further remove BOD, nutrients, pathogens, and parasites, and sometimes toxic substances.

•Primary treatment - theremoval of large objects - screening and sedimentation

• Resulting effluents have a high BOD values

Many wastewater treatment technologies are dependent on beneficial microorganisms for remediation of wastewater so that it won't detrimentally impact the environment.

One of the primary goals of biological treatment is the removal of organic material from wastewater so that excessive oxygen consumption won't become a problem when it is released to the environment.

Biological Wastewater Treatment

Another goal of biological treatment is nitrification/denitrification.

Nitrification is an aerobic process in which bacteria oxidize reduced forms of nitrogen.

Denitrification is an anaerobic process by which oxidized forms of nitrogen are reduced to gaseous forms, which can then escape into the atmosphere.

This is important because the release of nitrogen to the aquatic environment can also cause eutrophication (algal overgrowth).

Overview of nitrification and denitrification at the wastewater treatment plant.

• Anoxic digester:Removal of high molecular weight material; industrial wastewater

• Low production of biomass; most C is converted to CO2 and CH4

Secondary Treatment- Anaerobic

• Organic carbon is converted to CO2 and microbial biomass• Trickling filter - a bed of rocks(10-15 cm in diameter) at a 2m depth. The thick biofilm thatforms on the rocks oxidizesorganic matter• Activated sludge - 5 -10 hoursretention; flocs consisting ofbacteria (Zoogloea ramigera ) embedded in EPS(slime) and eukaryoticmicrobes• The sludge may be digestedanaerobically or dried andused as a fertilizer

Secondary Treatment- Aerobic

Tertiary Treatment- Removal of Inorganic Nutrients

• Most treatment facilities carry out only primary and secondary treatment

• Release of nitrate and phosphate - eutrophication of receiving water bodies

• Physical chemical processes: precipitation, filtration, chlorination

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