Felix offers a comprehensive range of Water Cycle Management Solutions, ranging from production and supply of drinking water to collection, treatment, recovery and recycling of wastewater. Its evolved expertise in Waste Water Treatment enables it to develop solutions that optimally meet the needs of municipalities, industrial houses and other concerns, including
Sewage treatment is the process of removing contaminants from wastewater, primarily from household sewage. It includes physical, chemical and biological processes to remove these contaminants and produce environmentally safer treated wastewater (or treated effluent).
A by-product of sewage treatment is usually a semi-solid waste or slurry, called sewage sludge, which has to undergo further treatment before being suitable for disposal or land application.
Sewage treatment may also be referred to as wastewater treatment, although the latter is a broader term which can also be applied to purely industrial wastewater. For most cities, the sewer system will also carry a proportion of industrial effluent to the sewage treatment plant which has usually received pretreatment at the factories themselves, to reduce the pollutant load.
If the sewer system is a combined sewer, then it will also carry urban runoff (storm water) to the sewage treatment plant. Sewage water can travel towards treatment plants via piping and in a flow – aided by gravity and pumps. The first part of filtration of sewage typically includes a bar screen to filter solids and large objects, which are then collected in dumpsters and disposed of in landfills. Fat and grease also are removed before the primary treatment of sewage.
Sewage is a mixture of domestic and industrial wastes. It is more than 99% water, but the remainder contains some ions, suspended solids and harmful bacteria that must be removed before the water is released into the sea.
The treatment of wastewater is divided into three phases: pretreatment, primary treatment and secondary treatment.
Large solids (with a diameter of more than 2 cm) and grit (heavy solids) are removed by screening. These are disposed of in landfills.
The water is left to stand, so that solids can sink to the bottom, and oil and grease can rise to the surface. The solids are scraped off the bottom, and the scum is washed off with water jets. These substances are combined to form sludge
The sludge is further treated in ‘sludge digesters’ –large heated tanks in which its chemical decomposition is catalyzed by micro-organisms. The sludge is largely converted to ‘biogas’, a mixture of CH4 and CO2, which is used to generate electricity for the plant. The liquid is treated by bacteria which break down the organic matter remaining in solution. It is then sent to oxidation ponds where heterotrophic bacteria continue the breakdown of the organics and solar UV light destroys the harmful bacteria.
A wide variety of analytical tests are used to determine the purity of the wastewater at various stages of treatment, so that the possibility of harm to either people or the environment is minimized.
Moving Bed Bio Reactor Systems consist of activated sludge aeration systems, where the BOD-COD consuming bacteria feed and multiply on the inner and outer surface of the inert media. This media acts as a large surface area for optimal contact between the bacteria, oxygen and influent water. With sufficient supply of oxygen, the bacteria culture breaks down the organic compounds in the influent, thus resulting in substantial reduction in the BOD & COD.
In this technology, the feed water to the DAF float tank is often (but not always) dosed with a coagulant (such as Ferric Chloride or Aluminum Sulfate) to coagulate the colloidal particles, and/ or a flocculant to conglomerate the particles into bigger clusters.
A portion of the clarified effluent water leaving the DAF tank is pumped into a small pressure vessel (called the air drum), into which, compressed air also is introduced. This results in saturating the pressurized effluent water with air.
The air-saturated water stream is recycled to the front of the float tank,which flows through a pressure reduction valve just as it enters the front of the float tank, resulting in the air being released in the form of tiny bubbles. Bubbles form at nucleation sites on the surface of the suspended particles, adhering to the particles. As more bubbles form, the lift from the bubbles eventually overcomes the force of gravity. This causes the suspended matter to float to the surface, where it forms a froth layer, which is then removed by a skimmer. The froth-free water exits the float tank as the clarified effluent from the DAF.
The MBR System consists of a submerged hollow tube.A PVDF micro-porous membrane is used to separate the treated water from the suspended growth-activated sludge process, resulting in purified water recovery. MBR Membranes have a pore size of ~0.2µm. Thus, most of the BOD, COD, TSS,etc of the influent are separated from the product stream.
A trickling filter, also called trickling biofilter /biofilter / biological filter / biological trickling filter, is a fixed-bed biological reactor that operates (mostly) under aerobic conditions. Pre-settled wastewater is continuously ‘trickled’ or sprayed over the filter. As the water migrates through the pores of the filter, organics are aerobically degraded by the biofilm covering the filter material.
Trickling filters are conventional aerobic biological wastewater treatment units, such as Active Sludge Systems or Rotating Biological Contactors. The advantage of all these systems is that they are compact. However, they are high-tech, and generally require skilled staff for construction and operation.
Trickling filters are a secondary treatment after a primary setting process (see also ‘septic tanks’ or ‘pre-treatment’).
The trickling filter consists of a cylindrical tank, and is filled with a highly specific surface areamaterial such as: rocks, gravel, shredded PVC bottles or special pre-formed plastic filter media. A highly specific surface provides a large area for biofilm formation. Organisms that grow in the thin biofilm over the surface of the media, oxidize the organic load in the wastewater to carbon dioxide and water, while generating new biomass. This happens mainly in the outer part of the slime layer, which is generally of 0.1 to 0.2 mm thickness.
The incoming pre-treated wastewater is ‘trickled’ over the filter with the use of a rotating sprinkler, prompting the filter media to go through cycles of being dosed and exposed to air.
However, oxygen is depleted within the biomass, and the inner layers may be anoxic or anaerobic.
The word filter is somehow misleading, as physical straining of solids is only marginal. The removal of organic substances occurs from bacterial action. Therefore, trickling filters are also called bios or biological filters, to emphasize the filtration aspect. Fixed film biological treatments also are used in other common treatment processes such as Rotating Biological Contactors of Fixed Film Activated Sludge Systems.