Queensland sedimentation and evaporation pond system (SEPS) trial

The Sedimentation and Evaporation Pond System (SEPS) is a low-capital effluent management system based primarily on shallow pond sedimentation of effluent solids and annual evaporation of the liquid to retrieve dried solids

Practical options for cleaning biogas prior to on-farm use at piggeries

Interest in the use of biogas from anaerobic digestion has been increasing within the Australian pork industry in recent years, driven by a significant potential for biogas use to buffer rising energy costs and to reduce carbon emissions from individual piggeries and across the whole pork industry. A recent life cycle assessment study suggested that a 64% reduction in piggery GHG emissions could be achieved by installing biogas capture and use systems. Further Government incentives have also contributed to the growing interest in on-farm biogas. One of the major obstacles to adoption of on-farm biogas technology in the Australian pork sector is the presence of relatively high concentrations of hydrogen sulphide (H2S) in raw piggery biogas, commonly in the range of 500 to 3000 ppm. Smelling like rotten eggs, H2S is highly toxic and corrosive. Exposure to H2S, even at relatively low concentrations, can result in severe human health impacts, while corrosion and increased maintenance of biogas use equipment necessitates some form of biogas treatment to remove H2S to suitable levels. Many of the existing biogas treatment technologies used in other industries are not ideally suited for on-farm application in the Australian pork industry, because on-farm systems must be relatively simple, low-cost, safe, robust and scalable, producing minimal hazardous waste products. However, a literature review, which examined various existing biogas purification technologies, identified biological oxidation of H2S and chemisorption with iron-based solid media as potential options for piggeries, provided that some key research and development gaps could be addressed. A particular issue with regard to chemisorption was the high cost of replacing commercial chemisorption medium (accounting for up to 5% of the savings derived from biogas use). Of further interest was the observation that the active components in commercial chemisorption media were also relatively common in natural materials such as soils, and even in some agricultural and industrial waste and by-products. However, such alternative chemisorption media required targeted laboratory and on-farm testing. With regard to biological oxidation, there was a need to determine whether the treated effluent outflow from a covered anaerobic lagoon could be used as a viable nutrient source in an external packed column system. This concept required testing on-farm. To assess chemisorption options, a detailed and carefully designed laboratory study tested and compared the H2S removal capacity of a commercial iron-based medium (cg5) with that of a range of low-cost alternative media. The results of these trials indicated a far superior performance of a commercial cg5 medium, probably due to its engineered high porosity and high iron content (the active ingredient). However, a locally sourced red soil was a potentially feasible alternative medium, with reasonable chemisorption capacity and likely low cost and ready availability, depending on the piggery locality. While the pressure drop through the red soil bed was ten times that of the commercial cg5 pellets, this was effectively reduced by mixing the red soil with a bulking agent (sugar cane mulch, SCM), albeit with a dilution of the active ingredient. An unexpected but highly favourable increase in H2S chemisorption capacity was observed following repeated regeneration of used red soil media by exposure to air, perhaps due to mechanical disruption or chemical reaction. The laboratory data was extended to on-farm trials which confirmed the performance of the red soil and cg5 media. Interestingly, the on-farm chemisorption performance of both media was superior to the laboratory results, possibly due to the ingress of traces of oxygen with the biogas, causing continuous regeneration. The on-farm performance of a low-cost, biological H2S treatment system was also tested, using treated CAL outflow as the liquid nutrient source sprayed over the column packing. The results were very promising, showing removal of over 90% of the H2S from the raw biogas, reducing H2S concentrations from 4,000 ppm to less than 400 ppm. The recycled CAL effluent proved to be an effective liquid nutrient source, without needing excessive air addition to meet O2 scavenging requirements of residual carbon in the liquid, and with no notable changes to the prevailing pH of the liquid in the biological vessel. These results suggested that a simple biological oxidation system has considerable potential as a low-cost option for removing bulk H2S from raw piggery biogas. Overall, the relatively low chemisorption capacity of the red soil+SCM medium suggested that it would not be suitable as a primary treatment medium, but with the highly effective biological treatment step first removing the bulk of the H2S, perhaps red soil mixtures could be feasible for polishing of biogas to a consistent quality. The potential economic viability of this scenario was assessed in a feasibility analysis given in the thesis. Further testing of red soil in tandem with biological oxidation is recommended, as are regeneration studies to establish the actual chemisorption capacity of red soil mixtures and viable means to regenerate these media

Bioenergy Support Program - DAF Transition Project 4C-116

Biogas systems are currently operating at 21 piggery units across Australia. Effluent from approximately 15% of the total Australian pig herd is currently directed to biogas systems which include 14 covered ponds (CAPs), 4 hybrid mixed/heated CAPs and 3 engineered vessel digesters. This is equivalent to 29% of the national herd housed in accommodation currently considered ‘suitable’ for biogas capture (exclude deep litter housing, outdoor production and smaller piggery units). Producers who have adopted biogas systems have reported significant financial benefits from energy cost savings, sale of surplus electricity to the grid, and returns from the sale of carbon credits and renewable energy certificates (RECs). In several cases, farm energy costs for the supply of electricity, LPG and diesel have been eliminated and capital expenditure payback periods less than three years have been reported. However, the majority of piggeries currently benefiting from biogas systems have capacities greater than 10,000 SPU (1000 sows farrow to finish), highlighting a need for continued development of biogas options for smaller piggeries, so they can also benefit. During the project term, the BSP assisted many producers, industry service providers and consultants with enquiries regarding piggery biogas system feasibility, planning, design, and even construction, commissioning and operation of biogas systems. The publications produced by the BSP have contributed substantially to reference/extension material available to support the ongoing safe and technically sound development of on-farm biogas systems. Scientific publications also evidenced the rigor of Pork CRC research in biogas. A national biogas survey indicated there were a substantial number of smaller producers interested in biogas and needing further information to assist adoption. The greatest concerns identified by producers with existing biogas systems were depleted biogas production, red tape, sludge management in CAPs, lack of industry support personnel and suppliers, and expensive generator maintenance

Installation of instrumentation for remote monitoring of biogas composition and operational data at commercial piggeries

New instrumentation was installed to closely monitor the operation of an existing hybrid covered anaerobic pond (hybrid CAP) at Piggery A, from April to June 2018. Over this period, the average biogas production from the hybrid CAP was 5,601 m3/d and the resulting biogas and methane yields were 523 m3 biogas and 287 m3 CH4, respectively, per tonne of volatile solids (VS) discharged into the hybrid CAP. The recorded methane yield indicated that the hybrid CAP was achieving a high methane recovery of 88% of the biochemical methane potential (BMP). Approximately two-thirds of the biogas produced by the hybrid CAP was used to run two 250 kWe combined heat and power (CHP) generator units, while the remaining third was burnt in a shrouded flare. The two CHP units generated an average of 6,490 kWh/d over the monitoring period (average output 270 kWe). Thirty-six percent (36%) of the electrical power generated by the CHP units was used in the pig sheds, predominantly running cooling fans, lights and heat lamps, 26% of the power was used to operate the on-site feed mill, and 26% was exported to the electricity grid. The remaining 12% (34 kWe) was used to run the hybrid CAP and onsite biogas production and use infrastructure. Piggery shed power consumption decreased and grid exports increased from April to June, reflecting the lower usage of the evaporative cooling fans as the weather became cooler. Based on the average power generation of 1.73 kWh/m3 biogas and the average biogas methane content of 55%, the average electrical efficiency of the generator engines was 34%, which is typical for reciprocating biogas engines. The average hydrogen sulphide (H2S) concentration in the biogas extracted from the hybrid CAP (223 ppm H2S) was much lower than levels typically observed in raw piggery biogas and only marginally higher than the recommended maximum of 200 ppm for many generator engines. However, this reduction in H2S concentration, which was achieved by biological oxidation inside the hybrid CAP headspace, was not sufficiently consistent for safe operation of the generator engines. Further biogas treatment in the external biological scrubber reduced the H2S concentrations to very low levels (average 18 ppm) which rarely exceeded 200 ppm. Occasional spikes in the H2S concentration generally coincided with generator stoppages which resulted in stoppages of the biological scrubber, biogas blower and air dosing pump. In general, the combined biological oxidation in the hybrid CAP and external biological scrubber was effective at removing H2S from the biogas

Validation of PigBal model predictions for pig manure production

PigBal is a mass balance model that uses pig diet, digestibility and production data to predict the manure solids and nutrients produced by pig herds. It has been widely used for designing piggery effluent treatment systems and sustainable reuse areas at Australian piggeries. More recently, PigBal has also been used to estimate piggery volatile solids production for assessing greenhouse gas emissions for statutory reporting purposes by government, and for evaluating the energy potential from anaerobic digestion of pig effluent. This paper has compared PigBal predictions of manure total, volatile, and fixed solids, and nitrogen (N), phosphorus (P) and potassium (K), with manure production data generated in a replicated trial, which involved collecting manure from pigs housed in metabolic pens. Predictions of total, volatile, and fixed solids and K in the excreted manure were relatively good (combined diet R2 ≥ 0.79, modelling efficiency (EF) ≥ 0.70) whereas predictions of N and P, were generally less accurate (combined diet R2 0.56 and 0.66, EF 0.19 and -0.22, respectively). PigBal generally under-predicted lower N values while over-predicting higher values, and generally over-predicted manure P production for all diets. The most likely causes for this less accurate performance were ammonium-N volatilisation losses between manure excretion and sample analysis, and the inability of PigBal to account for higher rates of P uptake by pigs fed diets containing phytase. The outcomes of this research suggest that there is a need for further investigation and model development to enhance PigBal's capabilities for more accurately assessing nutrient loads. However, PigBal's satisfactory performance in predicting solids excretion demonstrates that it is suitable for assessing the methane component of greenhouse gas emission and the energy potential from anaerobic digestion of volatile solids in piggery effluent. The apparent overestimation of N and P excretion may result in conservative nutrient application rates to land and the over-prediction of the nitrous oxide component of greenhouse gas emissions. © CSIRO 2016

Methane Recovery and use at Grantham Piggery

This report describes the outcomes from the Australian Methane to Markets in Agriculture (AM2MA) research project PRJ-005672 ‘Methane recovery and use at a piggery – Grantham’. This project involved upgrading the biogas extraction system originally installed in conjunction with a partial floating cover, retro-fitted to the primary anaerobic pond at the QNPH Grantham piggery under an earlier AM2MA project (Project No. PRJ-003003), as described by Skerman et al (2011). Following the system upgrade, this project also included installing a biogas reticulation pipeline to supply biogas from the extraction system, to a water heating system used to heat water circulated through underfloor heating pads in the piggery farrowing sheds. This biogas fired water heating system has the potential to significantly reduce on-farm energy costs by replacing a significant proportion of the Liquid Petroleum Gas (LPG) previously used for farrowing shed heating. Further monitoring of the biogas system performance has also been carried out. This report describes the work undertaken and outlines the monitoring results, implications, conclusions and recommendations arising from this work

Options for biogas cleaning and use on-farm

This project follows on from and utilises a floating cover currently being installed on the primary effluent pond at a southern piggery