New Zealand Journal of Marine and Freshwater Research abstracts

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Effluent characteristics of domestic sewage oxidation ponds and their potential impacts on rivers

CHRISTOPHER W. HICKEY

JOHN M. QUINN

ROBERT J. DAVffiS-COLLEY

Water Quality Centre
Division of Water Sciences
Department of Scientific and Industrial Research
P. O. Box 11-115, Hamilton, New Zealand

Abstract The effluent characteristics of 18 domestic sewage oxidation ponds designed to national specifications were examined. Measurements covering a wide range of parameters were made monthly over at least 1 year in ponds from three regions (Auckland, Manawatu, and Southland). There was considerable variation in effluent composition within ponds with time and between different ponds. Biochemical oxygen demand (BOD) concentrations (overall median 27 g irr³; 3-fold range of individual pond medians) showed less variation between ponds than concentrations of suspended solids (SS) (median 56 g nr³; 28-fold range). Available nutrient levels were very high (e.g., an overall median of 5.0 g nr³for dissolved reactive phosphorus and 7.1 g nr³ for dissolved inorganic nitrogen). Ammoniarepresentedapotential oxygen demand equivalent to the measured BOD. Chlorophyll a, as an index of algal biomass (only measured in Auckland ponds; median 0.89 g nr³; 4-fold range), showed some seasonality with higher concentrations in summer. Faecal coliforms (median 4300 100 ml"¹) showed large (200-fold) variability between ponds. Differences in pond effluent characteristics could not be attributed to influent loading as apercentage of design or to the significant temperature difference between regions. BOD, SS, and faecal coliforms did not appear to fluctuate seasonally. Only ammonium (NH₄-N) showed a consistent trend with season, with increased concentrations in winter. Maintenance of receiving water concentrations below existing criteria for 95% of the time would require >1100-fold dilution for coliforms (bathing criterion), > 115-fold for coliforms (post-treatment drinking water criterion), >950-fold dilution to prevent algal proliferations below discharges, and > 120-fold dilution to prevent clarity impacts on clear rivers. Criteria for most other aspects of river water quality are met if oxidation pond effluents are diluted >40-fold.

Keywords effluent; wastewater; oxidation ponds; lagoons; domestic sewage; water quality; rivers

New Zealand Journal of Marine and Freshwater Research, 1989, Vol. 23: 585-600 0028-8330/89/2304-O585$2.50/0 © Crown copyright 1989 Received 9 June 1989; accepted 3 August 1989

PDF file of entire paper: medium quality (1205K); (scanned from paper original: notes about this process)

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