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Landfill leachate is a growing problem in both Ireland and the rest of U.K. Methods of treating landfill leachate are often costly and ineffective but SRC willows are extremely capable of the bioremediation of landfill leachate. When screening Salix genotypes (120 in total) with landfill leachate, the majority of genotypes, responded well, with minimal stress. The data suggests that a number of genotypes maybe more suited to leachate than others. Commercial genotypes such as Nimrod and Olaf were particularly tolerant to leachate application. Various loading rates of leachate were applied to eight selected genotypes. The application rates were based on nitrogen content of the leachate. When evaluated, rates of around 1000 kg - 2000 kg N/ha/yr were optimal for biomass production with minimal phytotoxic effects. Application equivalent to 4000 kg/ha/yr produced a significant reduction in biomass yield and led to increased potassium concentration in the soil. Risk evaluation of the technology using simulated rainfall confirmed that the presence of willow actively reduces risk of N leaching and P run-off. Sulphate concentration was elevated in the willow planted plots. The application of leachate produced a small but significant effect on the combustion of the lignocellulosic biomass produced by willow. The minor changes to combustion did not significantly reduce the overall combustibility of the material. This suggests that pairing the bioremediation with methanogenic leachates with biomass production may be possible. This technology could be the sustainable and cost effective solution to a growing leachate problem, provided it is made accessible to landfill operators and local authorities. To increase uptake, it is necessary for policy to support bioremediation as a credible solution. Possibly, incentivising the use of phytoremediation in the way green technologies have been incentivised in recent years, could insure that landfills are not left with leachate treatment issues in the future.

The twin objectives of the Clean Development Mechanism (CDM) are to assist developing country host nations in achieving sustainable development, and to assist developed countries in meeting their greenhouse gases (GHG) emission reduction targets. This is achieved through implementing GHG abatement projects in developing countries. There has been increased attention in the contribution of CDM projects to sustainable development in host nations. Previous research has suggested that, when left to market forces, the CDM does not contribute effectively to sustainable development. One likely reason is that host nations define and evaluate projects contribution to sustainable development. This has led to a “race to bottom” with regard to setting sustainability standards triggered by a concern that project developers prioritise CDM investments in countries with lower sustainability standards. Researchers have identified the need for an international standard for assessing sustainable development benefits of CDM projects. The main aim of this research was to develop an international level framework for assessing sustainable development benefits of CDM projects with a specific focus on landfill gas (LFG) projects. An in-depth literature review was carried out to establish the link between sustainable development benefits of CDM projects in general, and LFG CDM projects in particular. A case study methodology was used to develop an understanding of landfill management practices at three existing landfill sites both in developed (n=1) and developing countries (n=2). The results from the literature review and case studies were utilized to develop the framework for assessing sustainable development benefits of LFG CDM projects. The developed framework comprises three sustainable development dimensions and 12 criteria with 16 matching indicators. Such a project specific assessment framework has not previously been developed. The results from the validation of the framework suggested that technology transfer is the most likely benefit of any LFG CDM project while balance of payments is the least likely benefit. The proposed framework can be utilised at two stages in a CDM project lifecycle. It can be used as: (i) a template to guide host nations’ Designated National Authorities (DNAs) on how to review projects before issuing Letters of Approval (LoA); and (ii) Designated Operating Entities (DOEs) can also use the developed framework to validate and verify that sustainable development benefits stated in project proposals have been realised at the project level.

Anaerobic digestion (AD) is an attractive waste treatment process in which both pollution control and energy recovery can be achieved. Source-segregated domestic food waste (FW) has a high organic content on a dry weight basis and is rich in lipids and proteins, indicating the potential for a good biogas yield with high methane content. Process instability, however, has often been reported in food waste digesters, which was mainly manifested by the accumulation of volatile fatty acids (VFA) and reduction of specific methane production. Trace element (TE) supplementation has been proved to be an effective way to rectify this problem and has been applied to industrial AD plants. This practice, however, was usually characterised by a trial-and-error approach due to the lack of a clear understanding of the impact of TEs on AD under different process conditions. The aim of this study was therefore to optimise TE dosing strategies for FW digestion at different loading rates, with particular attention to the role of cobalt (Co) and selenium (Se). The limiting concentrations of Co and Se were studied in long-term continuously stirred tank reactor (CSTR)-type digester experiments at organic loading rates (OLR) from 1.8 to 5 kg volatile solids (VS) m-3 d-1. In a digester operated at OLR 1.8 kg VS m-3 d-1 without TE addition, dosing of Co at a strength of 1 mg Co kg-1 fresh matter was effective to stimulate the complete degradation of accumulated VFA. Around 2500 mg L-1 VFA built up, however, after OLR increased to 2.5 kg VS m-3 d-1; then dropped slightly by addition of Se at a strength of 0.05 mg Se kg-1 fresh matter. After stepwise increases in Se concentration to 0.2 mg kg-1, VFA reduced to less than 1000 mg L-1. In another 2 digesters, at OLR 3 and 4 kg VS m-3 d-1 respectively, TE washing-out was introduced for determination of the limiting Co concentration. All TE supplementation was ceased in these 2 digesters for around 300 days with the exception of continuous addition of 0.2 mg kg-1 of Se. VFA accumulation up to 30000 mg L-1 occurred in one digester immediately after the OLR increased from 4 to 5 kg VS m-3 d-1 and later up to 22500 mg L-1 in the other digester when OLR increased from 3 to 4 kg VS m-3 d-1. By gradually increasing Co concentration in both digesters to 0.3~0.5 mg kg-1, VFA started to be consumed. At the end of test, the recovered digester with OLR 5 kg VS m-3 d-1 was running stably with 0.2 mg kg-1 Se and 0.3~0.5 mg kg-1 Co addition, with a pH of 7.8, IA/PA ratio 0.4, specific methane production (SMP) 0.47 standard temperature and pressure (STP) m3 CH4 kg-1 VS d-1, volumetric methane production (VMP) 2.37 STP m3 CH4 m-3 d-1, and VFA concentration less than 500 mg L-1. To further understand the effect of trace elements on VFA production, short-term trials were carried out to assess their function in VFA production. The results indicated that with accumulated VFA, supplementation of trace elements stimulated VFA production to a greater extent than VFA consumption. Effect of organic loading rate on TE dosing strategy and digester performance was studied in 5 digesters, all of which had stable operation but different trace element addition histories. One pair digesters was run as control at OLR 5 kg VS m-3 d-1 over the course of the experiment, another pair operated with a gradual loading increase to 6, 7, 8 and 9 kg VS m-3 d-1. A SMP of 0.46±0.02 STP m3 CH4 kg-1 VS d-1 at OLR 8 kg VS m-3 d-1 was achieved. Volatile solids destruction (VSD) rates were similar between OLR 5 and 8 kg VS m-3 d-1, at approximately 0.74~0.75, but reduced to 0.71~0.72 at OLR 9 kg VS m-3 d-1. Residual methane production (RBP) test results showed that biogas production of digestate from OLR 5 and 7 kg VS m-3 d-1 were similar, whereas digestate from OLR 9 kg VS m-3 d-1 generated more biogas than OLR 5 kg VS m-3 d-1, indicating lower conversion efficiency was achieved at OLR 9 kg VS m-3 d-1. Nitrogen mass balance equations were developed to distinguish nitrogen distribution in digesters. These showed that microbial biomass density increased along with OLR increase, which in turn requires an increase in TE addition. The specific rate of biomass increase at OLR 9 kg VS m-3 d-1, however, was lower than at 8 kg VS m-3 d-1, reflecting the decrease in specific methane production and VSD rate. The results indicate that FW digester was able to operate at OLR 8 kg VS m-3 d-1, without loss of performance when compared with OLR 5 kg VS m-3 d-1. Loading 9 kg VS m-3 d-1 was regarded as overloaded due to the lower hydrolysis and acidification efficiency. The fifth digester, in which the same TE dosing was applied, was operated with random loading: a daily load between 2.5~7.5 kg VS m-3 d-1 was randomly introduced while weekly average OLR was maintained at 5 kg VS m-3 d-1. Stable performance was observed in this digester with 2.27 STP m3 CH4 m-3 d-1 of 30-day rolling average VMP and 76% of VSD rate, and VFA concentrations less than 500 mg L-1. Further research on essential TE supplementation for stable FW digestion at high loading was carried out. All TE additions were ceased except 0.3 mg kg-1 of Co and 0.2 mg kg-1 of Se, in two pairs of digesters at loading 5 and 8 kg VS m-3 d-1, respectively. VFA accumulation occurred in digesters at the higher loading, which finally failed. VFA fluctuated around 4000 mg L-1 in digesters at OLR 5 kg VS m-3 d-1, until the rest of trace elements in a full 11 trace elements recipe were reintroduced, when VFA degraded quickly to below 1000 mg L-1. The research provided new insight on optimising essential TE supplementation to FW digestion, especially at moderate and high loading rates, to ensure stable and high productive biogas production.

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Increasing legislative and economic pressure to find more sustainable methods of organic waste management has fuelled innovation in biological treatment technology. By-products of paper manufacturing industries provide a large source of organic waste, which is known to have a high environmental impact. This waste paper sludge has been shown to be amenable to biological treatment. Recent research has confirmed that windrow-composting and vermicomposting techniques have potential to treat these wastes and share many economic and environmental benefits. Many authors have suggested that sludge specific composting methods need to be developed and this research aims to provide fundamental data in this respect. The treatment of specific waste paper sludges was investigated through small and larges calee xperimentsw ith the aim of optimising thesep rocessesw ith minimal intervention. Identical samples of a selected waste paper sludge feedstock were used in large scale investigations into the application of each composting technique, and the performance of each process and resulting products was evaluated. Windrow composting and vermicomposting were found to stabilise and enhance waste paper sludge in very different ways, producing unique products. In terms of processing, windrow composting resulted in more rapid rates of stabilisation and although the performance of the vermicomposting process was less effective in these respects, it afforded additional benefits as a treatment of waste paper sludge. Both processes were found to stabilise and enhance waste paper sludge but the selection of one system or the other will depend largely on the objectives of the project and the criteria required of the finished product.

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