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.

In emergency situations such as earthquakes, war, floods, etc., it is very imporant that sewage treatment is taken care of, because disposal of untreated human feces can result in the contamination of the ground and water and can provide breeding sites for flies and mosquitoes which may carry all kinds of infections. Feces also attracts domestic animals and vermin which increase the potential for the spreading of diseases.

Distribution of safe drinking water is essential for the protection of public health, but the importance of excrement disposal can’t be stressed enough. Diarrhea is responsible for 17% of ALL deaths of children under 5 years of age in the world. Over 85% of all deaths in african refugee camps are related to diarrhea.

Diarrhea diseases are most usually transmitted by feces being in touch with food or water through unwashed hands or when people drink from contaminated water sources. While proper hygiene and clean drinking water reduces diarrhea in many cases, the treatment of fecal waste plays the most important role in keeping the people healthy.

Reverse osmosis is an efficient technique for dewatering, concentrating or separating low-molecular-weight substances in wastewater. It can be used to concentrate all dissolved and suspended solid materials. The most important usage for reverse osmosis is desalination of seawater.

Osmosis is a physical process in which a solvent moves, without need of external energy, across a semi-permeable (allowing fluids or gases to pass or diffuse through) membrane (a thin sheet of natural or synthetic material), separating two solutions of different concentrations as the denser solution stays on the surface while the less dense goes through it. In reverse osmosis the solvent is forced through the membrane by applying pressure. This way even smaller particles such as salt ions can be separated because the use of pressure enables the use of membranes with more dense structure that wouldn’t let water pass through it using regular osmosis.

Nano-filtration is selected when Reverse Osmosis or ultrafiltration are not suitable. For example, nanofiltration can be used for demineralization.