Land treatment of slaughterhouse effluent : some microbiological and chemical aspects

Abstract

A review of literature relating to land treatment of wastewater was made. The available literature indicates that although land treatment of wastewater serves many useful purposes, such as the recovery of nutrients, irrigation of crops and replenishment of groundwater, there is a potential risk of spreading a number of pollutants including pathogenic bacteria and viruses in the environment. The literature survey also indicates that soul factors may affect renovation of wastewater. Due to the presence on interbedded terrestrial gravel layers beneath Christchurch, which contain high quality groundwater for domestic and industrial use and that Islington is in the recharge zone for groundwater whose flow line continues towards Christchurch City, an investigation was undertakes to see whether land treatment of slaughterhouse effluent at Islington meat works could cause groundwater pollution and disease hazards. Results from this investigation were used to suggest ways to improve the treatment of slaughterhouse effluent at the meat works.

In soil lysimeter study, field study and well water analyses, faecal coliform bacteria of water and soil samples were enumerated by membrane filtration method using M-FC medium (American Public Health Association et al., 1971), mineral N was determined by steam distillation method of Bremner(196S). BOD₅ of water samples in soil lysimeter study was determined by the Warburg manometric method (Umbreit, 1972).

Results of soil lysimeter study indicated that Selwyn loamy sand, Waimakariri silt loam and Taitapu clay loam varied in their ability to attenuate BOD₅, faecal coliform bacteria and mineral N found in slaughterhouse effluent. A 200 mm layer of Selwyn loamy sand may be used to cover the exposed stony area at Islington to treat slaughterhouse effluent.

Results of field study have shown that faecal coliform bacteria and mineral N may be washed through 650-900mm of soil by the applied slaughterhouse effluent.

Analyses of well water at Islington mean works have indicated the absence of faecal coliform bacteria and a concentration of mineral N of less then 5.0 g/m³. The results showed that well water at the meat works was not contaminated by pollutants derived from land disposal area.

In survival studies, faecal coliform bacteria on vegetation were enumerated by membrane filtration method using M-FC medium and MPN method was used to enumerate faecal cloiform bacteria in soil. Clostridium perfringens spores on vegetation and in soil were enumerated by the MPN method of the British Ministry of Housing and Local Government (1969). The results indicated that the average T₉₀ for faecal coliform bacteria on vegetation and in soil were 8 d and 33 d, receptively. The average T₉₀ for Cl. perfringens spores on vegetation and in soil were 35 d and 175 d, respectively. The principal factor affecting the survival of these micro-organisms was considered to be the presence of particulate matter deposited on the disposal area after irrigation. Weather was not found to have marked effect on the survival of these micro-organisms.

In conclusion, land treatment of slaughterhouse effluent at Islington poses some risk to groundwater pollution and animal health.