Preservation of Wastewater Effluent Samples for Forms of Nitrogen and Phosphorus

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Abstract
Samples of water containing concentrations of total organic carbon at levels greater than 20 mg/liter when preserved with 40 mg/liter of mercuric chloride did not provide a complete inhibition of microbiological growth. A complete inhibition was noted at a preservation level of 400 mg/liter of mercuric chloride. A study was conducted on chemical changes of forms of nitrogen and phosphorus in wastewater effluents preserved with 400 mg/liter of mercuric chloride. A variety of wastewater treatment plant effluent samples was combined into one composite. The composite was then divided into ten equal samples. Each sample was analyzed separately for Kjeldahl nitrogen, ammonia nitrogen, nitrite nitrogen, nitrate nitrogen, orthophosphate phosphorus, and total phosphate phosphorus after 10, 30, 60, 80, and 100 days. Due to a logistical handling problem, the samples were usually processed in order in batches. An analysis for total organic carbon, total inorganic carbon, and dissolved inorganic mercury was conducted after 100 days. Small but measurable differences were observed for all constituents from one period to another. The ammonia, nitrite, nitrate nitrogen system was most susceptible to change. The Kjeldahl nitrogen analysis showed the greatest variation among replicates and sets. The study indicated that wastewater samples can be stored at room temperature after preservation with 400 mg/liter of mercuric chloride for periods of up to 100 days with only minimal changes in the form of nitrogen and phosphorus.