The most common method of treating industrial waste water is open lagoons in which large man-made ponds or lagoons are provided for settlement and further biological improvement through storage of waste water.
Lagoons are constructed and lined with material, such as clay or an artificial liner that will prevent leaks to the groundwater below. This is a slow and cheap treatment system that can be used for various types of wastewater.
These lagoons rely on the interaction of sunlight, algae, microorganisms and oxygen. Most of the starch, palm oil and sugar industries employ lagoons to treat their waste waters. We have visited various industries, which employ even more than 10-step lagoon systems.
Lagoons are also aerated. Aerobic systems can achieve 80 to 90% removal of BOD with a retention time of 1 to 10 days. The basins may range in depth from 1.5 to 5.0 meters and use aerators. But due to the high electricity cost for aeration, most of the industries opt for anaerobic lagoons. Modern method of treating industrial waste water is by installing advanced anaerobic digestion plants. Modern high rate reactors can reduce the COD of the waste water by 85-95%.
Biogas produced will be used for heat or electricity generation. The most commonly used systems are UASB, AFFR, CSTR and CIGAR. Waste water from starch plants, palm oil plants, ethanol plants, poultry farms, cattle farms and piggery farms are ideal for biogas generation and power plants. Not all types of industrial waste water can be anaerobically treated. Extensive research in the field of treating such waste water anaerobically is being carried out in Asia.
Sewage refers to the municipal wastewater resulting from the mixing of waste waters from different sources disposed of, usually via a pipe or sewer and containing a broad spectrum of contaminants. If these liquid wastes are discharged into rivers, ponds, lands, etc., without proper treatment, it will result in offensive odour, pollution of water and air as they will emit gases like methane and carbon dioxide. By adopting environmental friendly technologies, these problems can be mitigated. These waste waters can be treated using numerous processes depending on the type and extent of contamination. A typical wastewater treatment plant includes physical, chemical and biological treatment processes.
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