% Molybdate reactive phosphorus of total phosphorus in urban wastewater influents and effluents in County Cork agglomerations >2000 P.E

Abstract

Phosphorus is a key nutrient in freshwater ecosystems as it is well known to cause severe water quality problems when enrichment with phosphorus occurs, a phenomenon known as eutrophication. Legislative measures are in place to control or limit the amount of phosphorus discharged, and there are several physical, chemical and biological treatment processes used to remove or reduce phosphorus prior to discharge. Whether or not rural developments are granted planning permission in Ireland is often contingent on the levels of phosphorus in the receiving waters it is proposed to discharge treated effluent to. Several forms of phosphorus exist in environmental monitoring; the most often encountered is the inorganic form usually known as orthophosphate. However, there are other names used for this inorganic form, depending on the method of analysis, such as soluble reactive phosphorus (SRP), molybdate reactive phosphorus (MRP), dissolved reactive phosphorus (DRP), leading to confusion and misinterpretation of results. The presentation of analytical data also leads to confusion when the results’ form is not clearly expressed. Average wastewater influent total phosphorus levels for County Cork’s wastewater treatment plants vary considerably. Average phosphorus loadings were in the range 2.3 to 14.2 mg/1 TP-P, although a more reliable upper end of the range for average influent TP-P in Cork is Ballincollig with 11.6 mg/1 TP-P. Average influent MRP ranged from 1.6 mg/1 to 7.6mg/l PO4-P. Average MRP% of the total phosphorus ranged from 43.5% to 68 %. Disregarding effluents where phosphorus removal measures are required under the Urban Waste Water Treatment Regulations, 2001, average effluent concentrations of total phosphorus ranged from l.lmg/1 at Kanturk to 6.4mg/l TP-P at Ballincollig. Average effluent concentrations of MRP ranged from 0.9 to 4.6mg/l PO4-P. The range of % MRP of the total phosphorus was greater in plants where phosphorus removal technologies were employed, 34.4% to 91.7%. Plants without additional phosphorus removal had a narrower range, 62.4% to 87.1%.