New Zealand Journal of Marine and Freshwater Research abstracts

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Effluent characteristics of dairy shed oxidation ponds and their potential impacts on rivers

CHRISTOPHER W. HICKEY

JOHN M. QUINN

ROBERT J. DAVIES-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 11 dairy shed 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 two regions (Manawatu and Southland) and covering two types of farms: town milk supply (non-seasonal) and daily factory (seasonal). There was considerable variation in effluent composition within ponds with time and between different ponds. Biochemical oxygen demand (BOD) concentrations (overall median 98 g nr³; 3-fold range of individual pond medians) showed less variation between ponds than suspended solids (SS) concentrations (median 198 g nr³; 9-fold range). Available nutrient levels were very high (e.g., an overall median of 12.2gm³ for dissolved reactive phosphorus and 75.0 gm³ for ammonium (NH₄-N)). The ammonia represents a 4-fold higher level of potential oxygen demand than the measured BOD. Faecal coliforms (median 70 000 (100 ml)¹) showed large variability both within and between ponds, with higher levels in town milk supply 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. Maintenance of receiving waterconcentrations below existing criteria for 95% of the time would require > 2 700-fold dilution for faecal coliforms (bathing criterion), > 67-fold dilution for coliforms (post treatment drinking criterion), and > 2700-fold dilution to prevent nuisance levels of algal proliferations below discharges. Most uses are accommodated provided dilution exceeds 250-fold requiring a minimum stream flow of 0.058 m³ s^for a220-cow herd.

Keywords effluent; wastewater; oxidation ponds; lagoons; dairy sheds; water quality; rivers

New Zealand Journal of Marine and Freshwater Research, 1989, Vol. 23: 569-584 0028-8330/2304-0569$2.50/0 © Crown copyright 1989 Received 7 November 1988; accepted 9 June 1989

PDF file of entire paper: medium quality (1323K); (scanned from paper original: notes about this process)

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