Botany · Ch 8 — Environmental Issues
Sewage disposal
Sewage disposal
Sewage disposal covers two related waste streams. Sewage — the faeces- and waste-water-laden effluent flowing from homes and factories through sewer systems — cannot be released directly into rivers and streams because of its heavy organic-matter and microbial load, so it is processed at sewage treatment plants (STPs) through physical, chemical and biological stages, generally organised as primary, secondary and tertiary treatment, before discharge as safer, less-polluting water; the greenhouse gases (CO2, methane, nitrous oxide) generated during this treatment process itself affect the atmosphere as well as urban and aquatic ecosystems, so upgrading to more advanced disposal-treatment technology helps cut both climate impact and pollution. Solid waste — all non-liquid waste causing health problems and an unpleasant living environment — is instead managed through landfill, incineration, recovery, recycling, composting and pyrolysis, with technological advances increasingly converting solid waste into renewable energy or organic manure rather than simply discarding it; electronic waste is a particular concern within this stream because it contains toxic, largely non-biodegradable materials, and the smoke released during its informal recycling and the leaching of its components pose serious threats to both human health and water bodies, which agricultural-landfill-type disposal methods are used to reduce. A separate liquid-waste stream includes point-source and non-point-source discharges such as storm water and …
What this figure shows. A process-flow diagram titled 'Sewage treatment plant process flow diagram', tracing raw sewage through two main stages. In primary treatment, sewage passes through screens and a comminutor to a grit chamber (grit is removed for disposal), then to a primary clarifier that separates primary effluent from raw/primary sludge, with the sludge routed to sludge treatment and disposal (including a return-sludge pump). In secondary treatment, the primary effluent passes through an aeration tank supplied by an air compressor (producing activated sludge), then a secondary clarifier and a disinfectant stage, producing secondary effluent that is either discharged to surface water or sent on to tertiary treatment if required. The diagram visually lays out the multi-stage sequence by which raw househ …
What this figure shows. A cutaway diagram of a sanitary landfill, showing its engineered cross-section: a base and cap of compacted solid waste, a network of leachate pipes running through the waste mass to collect leachate (contaminated liquid draining through the refuse) into a leachate storage tank and treatment system, a leachate-monitoring well and a separate groundwater-monitoring well to check for contamination, methane-gas recovery pipes that collect explosive methane gas generated by decomposing waste, and an electricity-generator building where the recovered methane gas is burned as fuel to generate electricity. The diagram illustrates how a modern sanitary landfill is engineered not just to bury waste safely but to actively capture and monitor i …