Sewage Filtration And Water Treatment

Waste water treatment systems can be divided into biological, physical and chemical processes. The microbiological processes can be separated into aerobic and anaerobic processes.

The purification of waste water produces large amounts of organic sludge, which has to be thickened, treated and disposed of. This is one of the most expensive parts of waste water treatment. This sludge is usually a inconvenient product as it will rot in the air, causing odor problems. Anaerobic processes rely on microbiological processes where organic material is degraded and biogas (composed of mainly methane and carbon dioxide) is pro­duced. Anaerobic processes take place in the absence of oxygen and produce much less excess sludge in a more stable (non-rotting) condition.

Conven­tional, aerobic waste water treatment has been exten­sively applied in industrialized countries, but has the reputation of being expensive and requiring specialist supervision. Aerobic waste water treatment is characterized by a high conversion ratio of soluble BOD into biomass, and thus sludge. Sludge is produced in large quantities, it is composed of mostly water, requiring relatively expensive de-watering, and it may contain pollutants, notably patho­gens and heavy metals, that render the use as fertilizer impossible or difficult. The excess sludge from aerobic treatment however, can be easily digested, yielding sufficient amounts of biogas to make the plant energetically autonomous and lowering operational costs.

Anaerobic waste water treatment has been introduced on full scale on various types of in­dustrial waste water for three decades, both in cold and warm climates. Results have been in most cases successful. Anaerobic processes, carried out in specially designed concrete or steel reactors, result in high quality and short retention times which generally equals reduced con­struction costs. An additional advantage of anaerobic treatment is that it produces a well-digested and stable sludge, which will not rot when exposed to air. It has favorable dewatering characteristics when compared to the “fresh” sludge from aerobic plants.