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Dairy factory wastewaters are increasingly being considered a valuable resource. However, these waters may also contain contaminants, natural or artificial, that may adversely affect the land to which they are applied. This review investigates dairy wastewaters, factors affecting their composition, some probable effects on land and compounds that may be used to trace the migration of pollutants.Dairy factory wastewaters differ depending on the types of products made by the factory and the treatment afforded wastewaters. In addition to milk and milk by-products, dairy factory wastewaters contain cleaning chemicals that contribute to the salt load, and synthetic compounds.From the limited studies where the effects on dairy processing wastewaters on land have been measured, the consensus of the literature results acknowledges the utility to agriculture can be highly variable and depends on the land to which it was applied and wastewater characteristics including concentrations of phosphorus, nitrogen, carbon and sodium. Excessive applications of nutrients such as nitrogen and phosphorus have resulted in runoff to nearby watercourses.Even fewer studies have investigated the use of organic marker compounds in the dairy industry. Lipids, terpenes and sterols found in the plants consumed by livestock would be useful for identifying pollutants from the dairy industry. However, a library of biological marker compounds and their likely sources is needed before such a technology could be applied more widely.

Untilled dairy pasture has the potential to release more phosphorus to the environment than a regularly ploughed pasture. In this paper we report the initial results of a study comparing the effects of cultivation, phosphorus (P) fertiliser (10, 35, and 100 kg P/ha), and two types of vegetation (ryegrass (Lolium perenne) or ryegrass mixed with clover (Trifolium repens)) in a randomised complete block design. Phosphorus was measured in soil samples taken from depths of 0–20 mm and 0–100 mm. Waters extracted from the 0–20 mm samples were also analysed. In all cases, the P concentrations (Olsen P, Colwell P, Total P, CaCl2extractable P, Dissolved Reactive P, and Total Dissolved P) in the top 20 mm declined with ploughing. Dissolved Reactive P measured in the soil water was 70% less overall in the ploughed plots compared with the unploughed plots, and by 35 weeks after P treatments the decrease in Dissolved Reactive P was 66%. The effects of the fertiliser and pasture treatments were inconclusive. The data suggest that ploughing can lower the risk of P exports from intensive dairy farms in the trial area.

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