Septic Systems

Many rural and suburban areas rely on septic tanks which are containers into which sewage flows. The solid material settles and is subject to microbial decomposition. The liquid is allowed to overflow and is distributed through a series of perforated piedes into the surrounding soil. As long as hoses are far enough arpat, the reduction of organic material is sufficient to reduce the concentrations of organic matter being released to levels that can be aacomodated without causing environmental harm.

Sewage Treatment Plants

Sewage that is piped to wastewater treatment plants is subjected to physical, microbial and soemtimes chemical processes. The aim is to reduce organic matter content and to lessen the biological oxygen demand. Most major cities have extensive sewage treatment plants. The border cities of Tijuana in Mexico and San Diego have developed an international agreement for jointly treating their wastewater. Sweage form Tijuana is piped across the border to a treatment plant on the US side of the border.

Primary phase:

This pahase involves physical separation of solid materials, largely through settling. The sludge can be treated in anaerobic digestors. Here, anaerobic bacteria and archaea further decompose the solid wastes, producing a stable solid material and methane that can be collected and used as a fuel.

Secondary phase:

In this phase, the liquid portion of the waste is subjected to microbial decomposition that is largely aerobic. Air may be be forced into tanks and the wastewater rigorously mixed to ensure aerobic conditions. An active microbial community devleops that degrades the organic compounds int he wastewater. A sludge forms that is allowed to settle.

Most of the sludge is removed for further treatment, but a portion containing high numbers of microbes is reintrudocued into the aerated treatment tank along with the next batch of wastewater to be treated. This ocmponent is called activated sludge because the microbes are already adapted to degrading the organic compounds in the wastewater.  The activated sludge process geenrally reduces the biological oxygen demand by 85-90%. It also greatly reduces the number of pathogens, which are largely out-competed by the nonpathogens and tend to settle in the sludge. The concentrations of Salmonella, Shigella, enteroviruses and other pathgogens are generally 9-99% lower in the effluent water that is discharged from the plant.

Tertiary phase (optional);

Sometimes prior to release, the water from the secondary treatment tanks is subjected to tertiary treatment. In this phase additional inorganic substances like ammonia, nitrate, phosphate and elimination of pathogens is done by chemical, physical or biological processes. Tertiary treatment removes nutrients that could support algal blooms and is important if the water is going to be released into a prstine laike. The teriary phage may also involve disinfection of the wasterwater as by filtration or chlorine treatment to eliminate pathogens.

Particular Techniques to Decontaminate Water

Oxidation: is one of the useful methods of waste water treatment, In this hydroxyl free radial (OH) is generated, which is highly reactive, non-selective oxidate which can destroy even the recalcitrant pollutants. Hydroxyl free radial generation is highly accelerated by combining ozone (O3), Hydrogen peroxide (H2O2), Titanium dioxide (TiO2), heterogeneous photo-catalysis, UV radiation or high electron beam radiation. (Joshi “Advances in Wastewater Treatment -A review” 2012.

Solar Water Disinfection: can be done by simply placing contaminated water in a transparent plastic bottles and leaving them in the sun for 6 hours. Ultraveiolet light kills bacteria and prarasites and inactivates viruses. It has been used primarily in impoversihed nations.

Red Tides & Alga Blooms:

The poisonous and destructive red times that occur frequently in coastal areas are often assocaited with dinoflgellates, whose pigments color the water. The blooms are most often triggered by excess nutrients form agricultural or other human activity. Red tides have a profound, determental effect on the fishing industry. Some 20 species of dinoflagellates produce powerful neurotoxins that inhibit the diaphragm, causing respiratory failure in many vertegrates. When the toxic dinoflagellates are abundant, many fishes, birds adn marine mammals may die. Humans consuming affected fish or shellfish will also be intesting neurotoxins that accumulate in the tissues of these animals.

Most dinoflogellates are photosynthetic unicells with two flagella. Dinoflagellates live in both marine and freshwater environments. Some dinoflagellates are luminous and contribute to the twikling or flashing effects one sees int eh sea at night, especially in the tropics, while other species contribute to the harmful algal blooms which can also lead to human disease. Plates made of a cellulose like material, often encrusted with silica, encase the dinoflagellate cells.