Lecture 8 Microbial Biotechnology Wastewater Sewage treatment Generally

Lecture: 8 Microbial Biotechnology

Wastewater / Sewage treatment Ø Generally, the wastewater discharged from domestic premises like residences, institutions, and commercial establishments is termed Sewage / Community wastewater. Ø It is made up of 99. 9% water and 0. 1% solids which are organic because it consists of carbon compounds like human waste and other organic matter. Ø Many industrial wastes are also organic in composition and can be treated physicochemically and/or by micro-organisms in the same way as sewage (biological treatment). Ø Wastewater treatment involves breakdown of complex organic compounds in the wastewater into simpler compounds that are stable and nuisance-free.

WHY SHOULD SEWAGE BE TREATED BEFORE DISPOSAL? q The decomposition of the organic materials contained in wastewater can lead to the production of large quantities of malodorous gases. q Untreated wastewater (sewage) contains a large amount of organic matter; if it is discharged into a river or stream, it will consume the dissolved oxygen for satisfying the Biochemical Oxygen Demand (BOD) of wastewater and thus deplete the dissolved oxygen of the stream; this will cause fish killing and other undesirable effects.

q Biological Oxygen Demand (BOD) is a measure of the oxygen used by microorganisms to decompose waste. q If there is a large quantity of organic waste in the water supply there will also be a lot of bacteria present working to decompose this waste. In this case, the demand for oxygen will be high (due to all the bacteria) so the BOD level will be high. As the waste is consumed or dispersed through the water, BOD levels will begin to decline. q Wastewater may also contain nutrients, which can stimulate the growth of aquatic plants and algal blooms, thus leading to eutrophication of the lakes and streams.

Eutrophication q In eutrophication the environment becomes enriched with nutrients. q It is the process by which a body of water acquires a high concentration of nutrients, especially phosphates and nitrates. q These typically promote excessive growth of algae. As the algae die and decompose, high levels of organic matter and the decomposing organisms deplete the water of available oxygen, causing the death of other organisms, such as fish. q Eutrophication is a natural, slow-aging process for a water body, but human activity greatly speeds up the process.

q Untreated wastewater usually contains numerous pathogenic, or disease causing microorganisms and toxic compounds; these may contaminate the land or the water body, q When fertilisers run-off into nearby water, they cause an increase in nutrient levels. q This causes phytoplankton to grow and reproduce more rapidly, resulting in algal blooms. q This bloom of algae disrupts normal ecosystem functioning and causes many problems.

q The algae may use up all the oxygen in the water, leaving none for other marine life. This results in the death of many aquatic organisms such as fish. q The bloom of algae may also block sunlight from photosynthetic marine plants under the water surface. q Some algae even produce toxins that are harmful to higher forms of life. This can cause problems along the food chain and affect any animal that feeds on them.

Nitrification and de-nitrification q Nitrification is the biological oxidation of ammonia into nitrite followed by the oxidation of the nitrite into nitrate. q Nitrate can be assimilated by plants through their roots and converted to organic form such as amino acids and proteins. q Ammonia (from decayed animals and plants) in the soil is used by bacteria such as nitrosomonas and nitrococcus as an energy source. They oxidize ammonia to nitrite. q Nitrite is oxidized by other bacteria, nitrobacter, to nitrate. q Nitrifying organisms are chemoautotrophs, and use carbon dioxide as their carbon source for growth. NH 3 + CO 2 + 1. 5 O 2 + Nitrosomonas → NO 2 - + H 2 O + H+ NO 2 - + CO 2 + 0. 5 O 2 + Nitrobacter → NO 3 -

Types of treatment sewage treatments • Mechanical treatment • Biological treatment • Chemical treatment

Biological treatment q Biological treatment is used primarily to remove the biodegradable organic substances in wastewater. q Basically, these substances are converted into gases that can escape to the atmosphere and into biological cell tissue.

3 stages of waste water treatment • Primary – solids are separated • Secondary – dissolved biological matter is converted into a solid mass by using water-borne bacteria – 95% of the suspended molecules should be removed • Tertiary – biological solids are neutralized then disposed, and treated water may be disinfected chemically or physically. There are 3 different disinfection process. 1. Chlorination 2. UV light radiation 3. Ozonation

Wastewater Treatment

Chlorination • Most common • Advantages: low cost & effective • Disadvantages: chlorine residue could be harmful to environment.

UV light radiation • Damage the genetic structure of bacteria, viruses and other pathogens. • Advantages: no chemicals are used • water taste more natural • Disadvantages: high maintenance of the UV-lamp

Ozonation • • Oxidized most pathogenic microorganisms Advantages: safer than chlorination fewer disinfection by-product • Disadvantage: high cost

3 different sludge treatments • Aerobic digestion • Anaerobic digestion • Composting

Aerobic digestion • • • Bacterial process Need oxygen Consume organic matter • Convert into carbon dioxide (CO 2) Anaerobic digestion • Bacterial process • • • Do not require oxygen Consume organic matter Produce biogas, which can be used in generators for electricity Composting • aerobic process • requires the correct mix of carbon, nitrogen, oxygen and water with • sludge Generate large amount of heat

Sludge disposal v Superheat sludge and convert into small granules that are rich in nitrogen § Sell it to local farmer as fertilizer v Spread sludge cake on the field v Save landfill space

v The wastewater treatment plant lab conducts a number of measurements and tests on the water. § suspended solids § B. O. D. § p. H § Temperature § Nitrogen § phosphorus v In addition to test performed at the wastewater lab, an off-site contract lab performs additional tests. § heavy metals § priority pollutants § W. E. T (Whole Effluent Toxicity) tests