New Zealand Journal of Agricultural Research abstracts

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Algal abundance, organic matter, and physico-chemical characteristics of dairy farm facultative ponds: implications for treatment performance

JAMES P. S. SUKIAS
CHRIS C. TANNER
ROBERT J. DAVIES-COLLEY
JOHN W. NAGELS

National Institute of Water & Atmospheric
Research Ltd
Private Bag 11 115
Hamilton, New Zealand

RONALD WOLTERS

Golder Associates (UK) Limited
54-70 Moorbridge Rd
Maidenhead, Berkshire,
England SL6 8BN, United Kingdom

Abstract  Six Waikato (New Zealand) dairy farm facultative ponds (DFPs), which met the larger sizes specified in recent dairy industry guidelines, were sampled monthly over an annual period. Median wastewater BOD5 was 65 g m^-3, suspended solids (SS) 206 g m^-3, ammoniacal N 37 g m^-3, total nitrogen 69 g m^-3, and faecal coliforms 24 000 (100 ml)^-1. This was 20-70% better than reported for DFPs built to previous guidelines, except for SS levels which were within reported ranges. However, performance was highly variable and only ¹/2 of the DFPs studied consistently met an effluent standard of <=100 g m^-3 BOD5 and only one reached <=150 g m^-3 SS. Removal of BOD5 was much lower than recorded for SFPs in New Zealand with equivalent BOD5 loading. Although the mean euphotic depth was only 0.11 m, algal biomass in DFPs was similar to that recorded for SFPs. Low phaeophytin concentrations and daytime oxygen exceeding 200% saturation in the shallow epilimnion on sunny days suggested a relatively healthy photosynthetic algal population was present in the DFPs. However, wastewater entering DFPs showed high median COD levels (1420 g m^-2). COD:BOD5 ratios of c. 12.1 (compared with 1.5-1.8 for SFPs) and BOD10:BOD5 ratios of c. 2 indicated the presence of a large pool of slowly degradable organic matter in the wastewater. This resulted in sustained exertion of BOD in the pond, explaining the "apparent" poor removal of BOD5 by DFPs. Conductivity was found to be a useful single-measure indicator of overall pond performance and management of sludge levels in the preceding anaerobic pond was identified as a key factor affecting DFP performance. Further improvements in dairy farm stabilisation pond performance are likely to be required on many farms to meet receiving water guidelines for the protection of water quality and aquatic life.

Keywords  wastewater; dairy effluent; waste stabilisation ponds; agricultural wastes; algal biomass; ammonia; sludge; pollution; environmental effects

New Zealand Journal of Agricultural Research, 2001, Vol. 44: 279-296

0028-8233/01/4404-0279 $7.00/0 (c) The Royal Society of New Zealand 2001

PDF file of entire paper: medium quality (1302K); (scanned from paper original: notes about this process)

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