Of course the anaerobic ...

Of course the anaerobic digestion of sewage sludge locally, with the benefit of energy recovery and local disposal of digestate and sludge cake is attractive environmentally. What is unattractive to the Water Utilities is the equipment capital cost, the risk to the Final Effluent quality and the ongoing operation, servicing and maintenance labour and management cost. The issues that arise are numerous:

1. Dewatering of indigenous sludges on rural STWs to provide a good dry solids % feed stock for an efficient anaerobic digestion process will generate the return of high load liquors to the existing process. If there is no biological treatment headroom or an ammonia consent in place then the works may also need its treatment capacity upgrading to treat the additional load. Or liquors return balancing will also be needed. This applies to mobile dewatering as well, and with the dramatic increase in EA fines for consent failures the risk to the Water Utility is very high. Fines of £300,000 for a rural sub 5 l/s STW have been levied in the recent past.

2. The land space available at many rural STWs will be constrained to build even micro size AD, CHP and liquor return balancing. Planning permissions will also need to be considered in respect to CHP noise (costly to mitigate) and also CHP emissions levels of NOX & SOX may need EA permitting. The physical area required for composting and the associated materials handling is also affected by these constraints.

3. The ongoing operation of these distributed plants will need a reverse in the trend of reducing the workforce to drive the Business Plan efficiency submitted to OFWAT in the five year AMP cycle. AD and associated plant and equipment needs regular maintenance and service of the equipment and the process needs to be constantly monitored to ensure it meets the HACCP criteria pathogen reduction so that the waste if the right quality to be put on agricultural land.

So, I believe the big picture is quite complex, and whilst I agree that the current inter-tankering practices are not the best for the environment, the solution sits outside of the current AMP cycle regulation of the Water Industry. By attempting to solve this in the current framework any Water Utility runs the risk of severely damaging itself by worsening performance in the areas measured by OFWAT. As a business sadly, your shareholders wouldn't see that as good management or governance. A degree of political imagination is required to enable a solution but unfortunately that is also something that is sadly lacking at the moment. The spreadsheet rules alas!