Organic matter in water :
The organic matter in fact is organic matter.They require oxygen for their waste water breakdown. This group includes oxygen demanding wastes, disease causing agent e-g sewage, synthetic organic compound, oil, industrial and runoff agricultural land etc.
All of these material undergo degradation by bacterial activities. In the presence of Dissolved Oxygen ( DO ). The presence of pollutants reduces light transmission through surface water, hence photosynthesis by marine plants.
Depletion in dissolved oxygen causes damage to water, birds, coastal plants and animals. In the other words, it damages marine life on massive scale and also affects of sea food which enters the human food chain.
Decomposition of organic matter :
There are two major pathways responsible for decomposing organics (plant residue, manures, synthetic organics, sewage sledges, etc.) in the soil-water environment. One pathway involves aerobic processes, and a second involves anaerobic processes.
During aerobic decomposition, carbohydrates are converted to carbon dioxide and water as follows:
CH2O + O2 → CO2 + H2O
where CH20 denotes carbohydrates, and therefore oxygen demand is relatively high, approximately 1.07 g of 02 per gram of carbohydrate. Furthermore, since organic waste contains various elements, a number of products (e.g., N0 3 , SO 4′ and PO4) are generated. During oxidative decomposition, assimilation processes by the microbial population also take effect:
5CH2O + → 3H2O +
where C5H7O2N denotes amino acid. Nitrogen assimilation by microbes requires 0.093 g NH3 per gram of CH2o. After rapid microbial cell synthesis subsides, NH3 appears, if N is in excess, by deamination,
C5H7O2 +5O2 → 5CO2 + 2H2O + NH3
followed by nitrification
NH3 + 2O2 → HNO3 + H2 O
It is a relatively slow process because of the slow rate of microbial growth. The process is compose of three stages.
1. Acid fermentation stage :
The first stage is known as the acid fermentation stage, lasts approximately 1 month, and simple, relatively low molecular weight organic acids are produced, decreasing pH to 4. The main organic acids produced during this stage include acetic, lactic, prop-ionic, and butyric.
2. Regression stage :
The second stage is refer to as the acid regression stage and it lasts 4-5 months. During this stage, organic acids are converted to methane, some metals Of metalloids may be methylated and converted to gases (e.g., methylated mercury, arsenic, selenium), and pH rises to 7.
3. Alkaline fermentation stage :
In the third stage, often refer to as the alkaline fermentation stage, solids break down slowly and gas evolution decreases significantly.