Biological parameters was rarely used as a parameter determining the pollution. In fact, measurements using physical and chemical parameters only provide momentary environmental quality and tend to give results with interpretation in a wide range. Today some developed countries such as France, Britain and Belgium glanced biological indicators for monitoring water pollution. Even already developed biotic water quality laws. In Indonesia has not had a biotic index of water quality standards, only the water quality standards for physical and chemical parameters.
Biological indicators are used to assess the macro changes in the ecological balance, especially ecosystem, due to the influence of waste. Species survival in an environment terpopulasi, will suffer physiological stress that can be used as biological indicators. Compared to using physical and chemical parameters, biological indicators can monitor continuously. This is because the community of aquatic biota (flora / fauna) spent his entire life in the neighborhood, so that in case of pollution will be accumulation or hoarding.
In addition, the biological indicator is the easy instructions to monitor pollution. The presence of environmental pollution, the species diversity will decline and the food chain to be more modest, except in the event of enrichment. Flora and fauna that can be used as biological indicators of river pollution can be observed from the diversity of species, the rate of growth of structure and sex ratio. Diversity of flora and fauna ecosystem of high river water quality of the river indicates good / not contaminated. But otherwise if diversity is small, the river is polluted.
Chemical Oxygen Demand (COD)
COD or Chemical Oxygen Demand is the amount of oxygen required to decompose all organic matter contained in water (Boyd, 1990). Chemical oxygen Demand (COD) or the chemical oxygen demand (COD) is the amount of oxygen required to oxidize organic substances present in water samples or the amount of oxygen required to oxidize organic substances into CO2 and H2O.
In this reaction almost any substance which is about 85% can be oxidized to CO2 and H2O under acidic conditions, while the biological decomposition (BOD) not all organic substances can be decomposed by bacteria. Figures COD is a measure of water pollution by organic substances can be oxidized naturally through microbiological processes, and result in a reduction of dissolved oxygen in the water.
COD is the amount of oxygen required to oxidize organic compounds in the water, so that the COD parameter reflects the amount of organic compounds chemically oxidized.
COD test is used to calculate the levels of organic material that can be oxidized by using strong oxidizing chemicals in acidic media. Some specific organic materials contained in waste water, resistant to biological degradation and some of them are poisonous although at low concentrations. Materials that can not be degraded biologically will be chemically degraded through oxidation, the amount of oxygen needed to oxidize is known as the Chemical Oxygen Demand.
COD levels in waste water decreased with decreasing concentrations of organic matter contained in waste water, low concentrations of organic matter that can not always be reduced by conventional processing methods. Figures COD is a measure of water pollution by organic substances that naturally can be oxidized and result in reduced oxygen dissolved in water. The concentration of COD in water must meet the quality standards that have been established so as not to pollute the environment.
Water that has been contaminated with organic waste prior to the reaction of yellow and after the oxidation reaction turned into green color. The amount of oxygen required for oxidation of the organic waste by the amount of potassium dichromate is used in the oxidation reaction.