There are many different types of processes that could be used to clean up wastewaters depending on the type of waste and contamination. Most wastewater is treated in industrial-scale energy intensive wastewater treatment plants (WWTPs) which include physical, chemical and biological treatment processes.
The most important aerobic treatment system is the activated sludge process*, based on the maintenance and recirculation of a complex biomass composed by micro-organisms able to absorb the organic matter carried in the wastewater. Anaerobic wastewater treatment processes (UASB, EGSB) are also widely applied in the treatment of industrial wastewaters and biological sludge. Tertiary treatment is being increasingly applied and most common technologies are micro filtration or synthetic membranes. Nitrates can be removed from wastewater via intensive microbial denitrification, for which specific additives are added to provide the bacteria with a source of carbon.
Disposal of waste waters from an industrial plant is a difficult and costly problem. Most petroleum refineries, chemical and petrochemical plants have onsite facilities to treat their wastewaters so that the pollutant concentrations in the treated wastewater comply with the local and/or national regulations regarding disposal of wastewaters into community treatment plants or into rivers, lakes or oceans. Other industrial processes that produce a lot of waste-waters such as paper and pulp production has created environmental concern, leading to development of processes to recycle water use within plants before they have to be cleaned and disposed.
Food industry
Wastewater generated from agricultural and food operations has distinctive as biodegradable and nontoxic, but that has high concentrations of biochemical oxygen demand (BOD) and suspended solids (SS). The constituents of food and agriculture wastewater are often complex to predict due to the differences in BOD and pH in effluents from vegetable, fruit, and meat products and due to the seasonal nature of food processing and post harvesting.
Processing of food from raw materials requires large volumes of high grade water. Vegetable washing generates waters with high loads of particulate matter and some dissolved organic matter. It may also contain surfactants.
Animal slaughter and processing produces very strong organic waste from body fluids, such as blood, urine and feces.
Processing food for sale produces wastes generated from cooking which are often rich in organic material , salt, oil and fats, acids or alkali.
Pulp & Paper industry
Effluent from the pulp and paper industry is generally high in suspended solids and BOD. Stand alone paper mills require primary treatment, such as sedimentation or dissolved air flotation. Increased BOD or chemical oxygen demand (COD) loadings, as well as organic pollutants, require biological treatment such as activated sludge or upflow anaerobic sludge blanket reactors.
Complex organic chemicals industry
A range of industries manufacture or use complex organic chemicals. These include pesticides, pharmaceuticals, paints and dyes, petrochemicals, detergents, plastics, paper pollution. Waste waters can be contaminated by feedstock materials, by-products, product material in soluble or particulate form, washing and cleaning agents. Treatment facilities that do not need control of their effluent typically opt for a type of aerobic treatment, i.e. aerated lagoons.
Water treatment
Many industries have a need to treat water to obtain very high quality water for demanding purposes. Water treatment produces organic and mineral sludges from filtration and sedimentation. Biological treatment will enable degradation of organic matter and sludge reduction.
*Activated sludge process
Activated sludge is a biochemical process for treating sewage and industrial wastewater that uses oxygen and microorganisms to biologically oxidize organic pollutants, producing a waste sludge containing the oxidized material.