Allbrook, R.F.Lowe, David J.Russell, J.M.Harfoot, C.G.McLay, C.D.A.Balks, Megan R.2026-09-142026-09-141995https://hdl.handle.net/10289/18640Meat processing plant effluent is a high-strength effluent comprising mainly organic materials including blood and fat. It is highly variable and often has high levels of suspended solids, biological oxygen demand, chemical oxygen demand, N and P. There is an increasing trend towards irrigation onto land for treatment and disposal of meat processing plant effluent. Perpetuation of a meat processing plant effluent irrigation scheme is dependent on maintaining adequate soil permeability on the land treatment area. A decline in soil permeability has been observed at a number of New Zealand meat processing plant effluent irrigation sites. If surface ponding of effluent and anaerobic conditions become widespread then odour and trafficability problems may become severe and it may become impossible to dispose of effluent without runoff. The main objectives of this thesis were to describe the occurrence and determine the mechanisms that lead to a decline in soil permeability at meat processing plant effluent irrigation sites. A reconnaissance survey of nine New Zealand meat processing plant effluent irrigation sites, from the King Country to Southland, was undertaken. At most sites, areas of soil surface crust development and effluent surface ponding were observed in topographic hollows and/or at the top ends of borders (where border dyke irrigation was practised). Surface crusting was associated with a build up in organic material, a decrease in soil bulk density and a decrease in infiltration rates. However, the survey demonstrated that land application of meat processing plant effluent was generally an effective means of dealing with large volumes of effluent. No long-term detrimental effects were identified, with surface crust development being regarded as a short-term problem that could be remedied, although sometimes at considerable cost to an effluent irrigation scheme operation. Laboratory and field experiments were designed to investigate the cause of soil permeability decline. A factorial laboratory experiment examined the effect of effluent type, volume of effluent added, soil type, time between effluent applications, temperature and rainfall on a range of soil and leachate properties. All of the factors tested had some impact on the soil or leachate properties that were monitored. However, effluent type and volume, and temperature, were the most important factors. High volumes of primary and untreated effluent caused the largest decline in soil permeability and were also associated with surface coat development. Soil permeability decreased more at 10 °C than at 25 °C and recovered more quickly at the warmer temperature. At 25°C soil drying and cracking led to increased macropore flow and a decrease in the effectiveness of effluent treatment. A field experiment was undertaken to compare the infiltration rates of untreated, primary treated, and anaerobically treated meat processing plant effluent with that of water. The infiltration rates of primary and untreated effluents declined faster than the infiltration rates of water or anaerobically treated effluent. The decrease in infiltration rate of primary and untreated effluents was attributed to physical pore blockage by the suspended solids in the effluent. A significant linear relationship (r = 0.97) was determined between infiltration rate and total cumulative suspended solids added. The linear relationship fits the model of Berend (1967), the coefficients of which were determined for primary and untreated meat processing plant effluent. Berend’s model was shown to have potential for use as a predictive tool to determine decline in infiltration rate as a function of effluent suspended solids content. To determine the magnitude of soil permeability loss and the rate of recovery, following effluent application, a laboratory experiment was carried out at 25 °C and 13 °C, using repacked soil cores. At 25 °C soil core permeability dropped by a mean of 70 % four days after effluent application, but recovered back to the initial level after 23 days. At 13 °C soil core permeability dropped by a mean of 50 % four days after effluent application, and took over 50 days to recover. It was concluded that the time taken for soil permeability to recover following application of large doses (200 mm) of primary treated meat processing plant effluent will be considerably longer in winter (approximately six weeks) than in summer (less than three weeks). Samples from effluent and water treated cores stored at 13 °C and at 25 °C, along with samples from field sites where meat processing plant effluent was regularly irrigated, were examined using a scanning electron microscope. There was a strong microbial response to addition of primary treated meat processing plant effluent to soils which resulted in formation of a semi-continuous coat on the soil surface. The surface coat developed under both field and laboratory conditions and formed and decomposed more quickly under warm moist conditions, taking 2 to 3 times longer to develop at 13 °C than at 25 °C. When allowed to dry out the coat did not decompose readily. A strongly developed continuous soil surface coat was present in areas where effluent had ponded in paddocks and was also present in areas where water ponding occurred, such as adjacent to water troughs. It was concluded that the decline in soil permeability observed as a result of application of New Zealand meat processing plant effluents, at the sites investigated, was caused by development of a soil surface coat which was formed from both, the suspended solids from the effluent, and, the microbial materials that develop in response to effluent application. The implications for management of soils receiving meat processing plant effluent are discussed.enAll items in Research Commons are provided for private study and research purposes and are protected by copyright with all rights reserved unless otherwise indicated.Thesis