Power consumption by the UK water industry has increased as a result of the introduction of new quality standards; the annual (2008/2009) carbon dioxide output was reported at 5·1 Mt. Biogenic output of carbon dioxide for the sector was calculated to be about 2 Mt. The strategies available to the water industry for reducing carbon footprint are increased use of renewable energy, principally anaerobic digestion, using less power and methods for reducing carbon dioxide emissions. This paper reports on work sponsored by UK Water Industry Research to examine methods for capturing and utilising carbon dioxide from wastewater treatment. The review has concluded that bioconversion and biofixation using algae and hydrogenotrophic methanogenesis are the most promising methods for utilising carbon dioxide. These technologies would readily integrate into existing industry flow sheets and both increase biogas production and reduce carbon dioxide emissions.

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The implementation of community-level de-centralised anaerobic digestion (AD) systems offers a sustainable solution for organic waste management and energy provision, but there is currently a need for low-cost methods of system control and management at this scale. The problem becomes accentuated with increasing deployment, as greater complexities are created by the need to both monitor and control a wider network of smaller, community-scale plants. This paper describes research to design, deploy and test such a system by creating a network of two independent biogas generation AD reactor sites situated in the United Kingdom and Thailand. Internet of things (IoT) aspects such as inexpensive and widely available open-source control electronics was used in combination with small commercial gas analysers to log, transfer and share data with a central station, achieving real-time monitoring of performance for both networked digesters. The design proved beneficial for collaboration and knowledge exchange purposes along with providing off-site observations on reactor status. This information was used for early intervention to maintain biogas yields and enable the dynamic assessment of process economics. The concept showed potential for upscaling to larger multi-site networks of AD reactors that could maintain process optimisation without the need for skilled staff on site.

Operational data from an anaerobic wastewater treatment plant (expanded granular sludge bed (EGSB) reactor) were analysed before and after a defect with the solids separator. The results presented suggest that a newly available method for the analysis of total volatile fatty acids (VFAs) was ideal as a rapid, onsite, operational indicator of reactor stability. These total VFAs were shown to provide an earlier warning of the separator problem than the other rapid routine methods of monitoring digesters such as alkalinity and suspended solids. Chemical oxygen demand (COD) removal, pH and gas yield were not as useful for monitoring because of their slow response. The results are from a high rate reactor; the loads were 18 kg COD/m 3 /d in the first year and 26 in the second with 4·4 d hydraulic retention time.The results for both years of operation demonstrate a 95% conversion of COD into gas with an additional contribution from solids digestion (specific gas yield of 0·4 l methane (CH 4 )/g COD rem ). This high performance was attributed to the solubility of the COD and the efficient EGSB mixing.

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