Sewage Treatment and Water Conservation

• Clean water is a scarce resource so must be conserved.
• Solutions are sewage treatment, reducing water pollutants, and conserving water use, especially in agriculture.

Sewage Treatment

• Water treatment plants (sewage treatment plants) treat sewage before returning it to the environment.
• The degree of water treatment determines its return, like using treated sewage water for irrigation to lower agriculture costs.
• Sewage treatment includes primary and secondary treatments.
• Primary treatment removes solid materials in tanks where heavy particles settle.
• Secondary treatment uses microorganisms to break down remaining wastes and may add chemicals like chlorine to kill pathogens.
• Primary treatment starts by screening the water to remove debris and insoluble solid particles.
• Screened sewage passes through a chamber where grit particles (stone, sand) and insolubles sink.
• The liquid goes to a sedimentation tank for semisolid organic sludge to settle.
• Sludge is treated separately as the liquid goes through secondary treatment.
• Secondary treatment uses the trickling filter (biological filter) or activated sludge process; both use microorganisms to break down sewage particles.
• In the biological filter method, a rotating pipe sprays liquid wastewater onto porous rocks coated with aerobic microorganisms, forming ecosystems.
• Microbes such as aerobic bacteria degrade dissolved organic matter and protoctists that feed on bacteria.
• Water trickles through the porous beds so microorganisms break down organic material and pathogens.
• The treated water then goes to another sedimentation tank and is discharged or used for irrigation.
• In the activated sludge method, aerobic microorganisms forming complex food chains are used in an aeration tank through which air is bubbled, instead of coating stones.
• Wastewater runs through the aeration tank, is passed to another sedimentation tank, and the resulting liquid is moved to the environment.
• Sewage sludge has organic material that sinks in settlement tanks.
• It can be dried for fertilizer or decomposed by anaerobic digester.
• Decomposing sludge in an anaerobic digester using anaerobic bacteria (without air) generates biogas (methane).
• This gas can be stored and used to operate the sewage treatment plant.

Reduction of Water Pollutants from Farmland Runoff

• Pesticides, fertilizers, and animal wastes that wash into bodies of water severely pollute water.
• Strategies can be used to reduce the amount of these pollutants.
• Natural pest control (using beneficial organisms that eat harmful pests) reduces pesticide concentrations.
• Ladybugs eat aphids and other insects and are therefore used by farmers to lower pest numbers.
• Reducing fertilizer pollution involves using less fertilizer overall, improving fertilizer application timing, and using less harmful fertilizers.
• Applying minimum fertilizer amounts reduces fertilizer runoff.
• Reducing/eliminating fertilizer application before irrigation/rainfall reduces runoff, as water washes fertilizers into water bodies.
• Organic fertilizers (manure) have fewer nitrates than artificial fertilizers, so they can be used instead of artificial fertilizers to reduce water pollution.

Clean water is a scarce resource, so it is important to conserve it. Sewage treatment plants help treat sewage before returning it to the environment. Sewage treatment includes primary and secondary treatments to remove solid materials and break down remaining wastes.