Nutrient Removal from Secondary Effluent by Alum Flocculation and Lime Precipitation.

The removal of phosphorus and nitrogen compounds from biochemically treated wastewater effluents by alum flocculation and lime precipitation was investigated. Samples of secondary effluent were flocculated or precipitated in accord with conventional Jar Test procedures. The phosphorus removal was found to be highly pH dependent with an optimum pH of 5.57 ± 0.25. At this pH an alum dose of 250 mg/l. removed 95 per cent of total phosphorus, 55 per cent of the chemical oxygen demand, 60 per cent of the organic nitrogen, 25 per cent of the NO3--N and NO2--N, 17 per cent of the apparent ABS and none of the ammonia-N. A dose of 600 mg/l. Ca(OH)2 raised the pH of the sample to 11.0 and removed 99 per cent of the total phosphorus. The estimated chemical costs for removal of 95 per cent of the phosphorus by lime and alum were 32 and 73 $MG (dollars per million gallons), respectively. 1 . I N TRO D U C TI O N ONE of the major problems caused by discharging biochemically treated wastewater effluents into lakes and streams is the eutrophication of these waters. This eutrophication is generally attributed to the discharge of fertilizing elements such as phosphorus and nitrogen. The removal of phosphorus and nitrogen from sewage effluents appears to be a practical way of limiting algal blooms in the receiving waters. The removal of these elements by biochemical or chemical means appears to be feasible. Various laboratory and field studies, SAWYER(1944), FENG (1950), WUHRMANN (1960), LUDZACK and ETTINGER (1962), have shown that the biochemical wastewater treatment processes can be modified such that significant removal of nitrogen and/or phosphorus can be attained. Chemical precipitation or flocculation of biochemically treated wastewater effluents have been investigated by RUDOLF (1947), OWEN (1953), LEA et al. (1954). These investigations have been discussed by STUMM (1962). In general these investigations have shown that significant amounts of phosphorus can be removed from secondary effluents by alum and iron flocculation or lime precipitation. ROHLICH (1963) has recently reviewed methods of phosphorus and nitrogen removal from sewage plant effluent. In the past 10-15 years since these studies were conducted, the composition of treated sewage effluent has changed considerably. The proportion of the condensed phosphate in the total phosphorus as well as the total phosphorus has increased. In addition, the concentration of organics, and in particular, surfactants, e.g. ABS, has increased significantly during this period. Since there is growing concern with respect to eutrophication of natural waters by * Condensed from Nutrient Removal from Secondary Effluent by Alum Flocculation and Lime Precipitation, S. K. Malhotra, Ph.D. Thesis, University of Wisconsin, 1962.