Anaerobic pond treatment of pig farm manure slurry in Aotearoa New Zealand : a case study : exploring opportunities for enhanced performance. (2022)
Type of ContentTheses / Dissertations
Thesis DisciplineCivil Engineering
Degree NameMaster of Engineering
Pork production is a relatively small part of Aotearoa New Zealand’s important agricultural sector, but manure slurry from pork production gives rise to several environmental challenges, such as odour, eutrophication from wastewater discharges containing high nutrient loading, and the release of greenhouse gases. One way to mitigate the environmental effects is to treat the manure slurry in anaerobic digestion pond systems. Although a functioning pond, together with collection and combustion of the produced methane, does reduce the environmental impact, there are many cases where systems fail. One possible cause of system failure is fats in the manure slurry from the pigs, which in turn is dependent on the pig feed. Fat in anaerobic digestion systems is known to cause issues, such as foaming and uneven methane production. The main objective of this research was to, in the field, measure the performance of the waste treatment system on a pig farm in Aotearoa New Zealand and, in the laboratory, investigate the effect of dairy by-product on methane potential. Fieldwork was carried out to characterise the pond system of the farm and explore possible seasonal variations. Several important parameters, such as Total Kjeldahl Nitrogen (TKN), volatile solids (VS) and phosphate were measured for the manure slurry and pond digestate. Laboratory experiments, using bench-scale reactors, were carried out to measure the methane potential of solutions of manure slurry to inoculum ratios (g VS) of 1:1 and 0.5:1 and first pond digestate to inoculum ratio (g VS) of 1:1. Another laboratory experiment, also using bench-scale reactors and a solution of manure slurry to inoculum ratio (g VS) of 0.5:1, was carried out to measure the effect of concentrations of 5 %, 10 % and 15 % dairy by-product on methane potential. From the seasonal study it could be seen that the concentrations of most parameters analysed in the manure slurry varied widely between sampling occasions, whereas the concentrations were more consistent in the two ponds. The only parameter that showed significant difference between summer and winter months was phosphate with increased concentration in manure slurry and decreased concentration in digestate from the second pond during the summer months. A possible explanation for increased phosphate concentrations in manure slurry is the use of phosphate rich dairy by-product in the pigs’ feed during the summer months. For the digestate from the second pond, a possible explanation for the decreased concentration of phosphate could be struvite formation during the summer months. The laboratory experiments investigating two different ratios of manure slurry showed that the methane concentration and cumulative methane produced varied more between samples for manure slurry of the inoculum ratio 1:1 (g VS) solution than for the 0.5:1 solution, probably due to higher heterogeneity of the material. The laboratory experiments of co-digestion of manure slurry and three different concentrations of dairy by-product showed a longer lag phase for methane production, more build-up of crust and less degradation of organic material for higher concentrations of dairy by-product. The overarching conclusion of the study is that there are indications of overload issues in the waste system and one way to address this could be to increase hydraulic retention time by changing flow order of the ponds, and to discard leftover dairy by-product elsewhere.
RightsAll Right Reserved
Showing items related by title, author, creator and subject.
Anaerobic pond treatment of pig farm effluent in New Zealand: exploring opportunities for enhanced performance Nilsson A; Bello Mendoza R; Masten S; O'Sullivan, Aisling (2020)The objective of this project is to explore ways to enhance the performance of covered anaerobic ponds to increase methane production, reduce odour emission, and improve digestate quality. The methane production and ...
REGIONAL STRATEGY 2020 to 2030 : Durable Eucalypts: a multi-regional opportunity for New Zealand’s drylands: focus areas and action/goals for 2019-2022 Millen P; Buck K; Palmer H; Altaner, Clemens (2019)EXECUTIVE SUMMARY The NZDFI has developed this regional strategy to provide a rationale and overview of its planned activities over the next three years and beyond. The strategy identifies six key focus areas where ...