Performance evaluation of two dairy shed waste management systems in the Southern Highlands of NSW

Rapid changes in regulation, catchment water quality, and public perception are the main driving forces towards more sustainable dairy farming in the Southern Highlands, NSW. A study was undertaken to assess the performance of two established waste management systems in terms of on-farm nutrient control/containment. The systems were installed in the mid-1990s as part of a pilot program to develop best management practice (BMP) pollution control techniques; however they are now considered to be below current BMP standards. The first was a treatment system consisting of stabilisation ponds and constructed wetlands designed to provide low-energy treatment before effluent is (legally) discharged into a creek. The second was a direct application to land system that irrigates raw wastewater onto a designated paddock throughout the year under all weather conditions. Seasonal monitoring of the ponds and wetland treatment system indicated effective pollutant removal throughout the year, achieving net pollutant removals of 94%, 87%, 93%, 67% and 25% for TSS, COD, BOD 5 , TKN and TP, respectively. A theoretical water balance revealed that addition of 4700 L/d of uncontaminated water was causing notable impairment to the removal efficiency of the system. The performance of the system was also inhibited by excessive sludge accumulation in the anaerobic pond stage, and deficient vegetation, algal growth and P saturation of the substrate in the constructed wetlands. Performance data from the ponds and wetlands were fitted to flow-adjusted first order complete-mix and plug flow models, respectively. of the Arrhenius temperature dependence equation revealed that removal of TSS, COD and BOD 5 in the ponds was positively related to temperature ( θ = 1.209, 1.182 and 1.126, respectively), while temperature had the converse effect on TS and COD removal in the wetlands ( θ = 0.966 and 0.951, respectively). Disposal of the effluent from the treatment system is allowing the release of 350 kg/yr of nitrogen and 88 kg/yr of phosphorus directly into a natural creek, which is resulting in measurable degradation of water quality downstream of the discharge point. Upstream TKN and TP concentrations averaged 0.82 and 0.06 mg/L, respectively, while downstream of the discharge the mean Abstract according to a typical pasture management regime. Surface runoff was also captured from both the effluent-treated ( treated ) and untreated sites to investigate nutrient export from the waste application site. The general outcome of the soil analyses was to show that wastewater application is positively affecting the available nutrient pool, but on the whole is exhibiting no greater impact on soil properties than other land use factors such as intensive stocking and pasture improvement. Significant increases in soil nutrient concentrations resulting from waste application were associated with more mobile plant-available nutrient species including extractable phosphorus, nitrate and potassium, which are mostly by-products from natural decomposition of the organic fraction of the applied waste. Otherwise, waste application had no bearing on the net nutrient status of the soil in terms of TP, TN, CEC, and organic matter. monitoring indicated that mean concentrations of all forms of nutrients were significantly higher in surface runoff from the treated site than in runoff from the untreated site. TKN, NH 3 -N, TP and DRP concentrations averaged 3.36, 0.77, 0.89 and 0.69 mg/L, respectively, from the untreated site, while the same parameters averaged 20.56, 8.60, 7.77 and 6.44 mg/L, respectively, on the treated site. Concentrations were related to rainfall quantity but not intensity indicating that mechanisms of desorption and dissolution governed nutrient export from effluent treated pasture. Thus contamination of surface runoff was indicative of short-term impacts related to direct wash-off of nutrients from applied waste rather than endemic problems associated with over enrichment of the receiving soil. The evaluation identified major shortcomings associated with the two forms of waste management system under review. Significant modifications to both systems are required in order to achieve complete nutrient containment as required to satisfy regulatory standards. Further research is recommended to determine whether adherence to best management practice (BMP) will prevent nutrient losses and to improve strategic distribution of the nutrient content of dairy