Chemical characteristics Wastewater quality indicators

1 chemical characteristics

1.1 hydrogen
1.2 oxygen
1.3 nitrogen
1.4 phosphates
1.5 chlorine

chemical characteristics

virtually chemical may found in water, routine testing commonly limited few chemical elements of unique significance.

hydrogen

water ionizes hydronium (h3o) cations , hydroxyl (oh) anions. concentration of ionized hydrogen (as protonated water) expressed ph.

oxygen

most aquatic habitats occupied fish or other animals requiring minimum dissolved oxygen concentrations survive. dissolved oxygen concentrations may measured directly in wastewater, amount of oxygen potentially required other chemicals in wastewater termed oxygen demand. dissolved or suspended oxidizable organic material in wastewater used food source. finely divided material readily available microorganisms populations increase digest amount of food available. digestion of food requires oxygen, oxygen content of water decreased amount required digest dissolved or suspended food. oxygen concentrations may fall below minimum required aquatic animals if rate of oxygen utilization exceeds replacement atmospheric oxygen.

basically, reaction biochemical oxidation may written as:

oxidizable material + bacteria + nutrient + o2 → co2 + h2o + oxidized inorganics such no3 or so4

oxygen consumption reducing chemicals such sulfides , nitrites typified follows:

s + 2 o2 → so4


no2 + ½ o2 → no3

since natural waterways contain bacteria , nutrient, waste compounds introduced such waterways initiate biochemical reactions (such shown above). biochemical reactions create measured in laboratory biochemical oxygen demand (bod).

oxidizable chemicals (such reducing chemicals) introduced natural water initiate chemical reactions (such shown above). chemical reactions create measured in laboratory chemical oxygen demand (cod).

both bod , cod tests measure of relative oxygen-depletion effect of waste contaminant. both have been adopted measure of pollution effect. bod test measures oxygen demand of biodegradable pollutants whereas cod test measures oxygen demand of biodegradable pollutants plus oxygen demand of non-biodegradable oxidizable pollutants.

the so-called 5-day bod measures amount of oxygen consumed biochemical oxidation of waste contaminants in 5-day period. total amount of oxygen consumed when biochemical reaction allowed proceed completion called ultimate bod. because ultimate bod time consuming, 5-day bod has been universally adopted measure of relative pollution effect.

there many different cod tests of 4-hour cod common.

there no generalized correlation between 5-day bod , ultimate bod. there no generalized correlation between bod , cod. possible develop such correlations specific waste contaminants in specific wastewater stream such correlations cannot generalized use other waste contaminants or wastewater streams. because composition of wastewater stream different. example effluent consisting of solution of simple sugars might discharge confectionery factory have organic components degrade quickly. in such case, 5 day bod , ultimate bod similar since there little organic material left after 5 days. final effluent of sewage treatment works serving large industrialised area might have discharge ultimate bod greater 5 day bod because of degraded material have been removed in sewage treatment process , many industrial processes discharge difficult degrade organic molecules.

the laboratory test procedures determining above oxygen demands detailed in many standard texts. american versions include standard methods examination of water , wastewater.

nitrogen

nitrogen important nutrient plant , animal growth. atmospheric nitrogen less biologically available dissolved nitrogen in form of ammonia , nitrates. availability of dissolved nitrogen may contribute algal blooms. ammonia , organic forms of nitrogen measured total kjeldahl nitrogen, , analysis inorganic forms of nitrogen may performed more accurate estimates of total nitrogen content.

phosphates

total phosphorus , phosphate, po−3

4

phosphates enter water ways through both non-point sources , point sources. non-point source (nps) pollution refers water pollution diffuse sources. nonpoint source pollution can contrasted point source pollution, discharges occur body of water @ single location. non-point sources of phosphates include: natural decomposition of rocks , minerals, storm water runoff, agricultural runoff, erosion , sedimentation, atmospheric deposition, , direct input animals/wildlife; whereas: point sources may include: waste water treatment plants , permitted industrial discharges. in general, non-point source pollution typically higher point sources of pollution. therefore, key sound management limit input both point , non-point sources of phosphate. high concentration of phosphate in water bodies indication of pollution , largely responsible eutrophication.

phosphates not toxic people or animals unless present in high levels. digestive problems occur extremely high levels of phosphate.

the following criteria total phosphorus recommended u.s. environmental protection agency.

phosphorus low (< 1 mg/l) in clean potable water sources , not regulated;

chlorine

chlorine has been used bleaching, disinfectant, , biofouling prevention in water cooling systems. remaining concentrations of oxidizing hypochlorous acid , hypochlorite ions may measured chlorine residual estimate effectiveness of disinfection or demonstrate safety discharge aquatic ecosystems.