Proceedings

Anaerobic ponds (APs) have the potential to provide many advantages for wastewater treatment in the UK, including low energy demand, minimal operation and maintenance requirements including sludge management, and the potential for renewable energy production. In order to quantify and examine the merits of incorporating APs into decentralised wastewater treatment for the UK water sector, a flowsheet modelling approach has been adopted to compare an AP flowsheet to a current standard decentralised flowsheet. An example works of 2,000 PE was chosen with a per capita flow rate of 200 L d-1 and a weak strength wastewater to reflect combined sewerage influent. Life-cycle cost assessment (LCCA) was conducted on the two flowsheets assuming a 20 year M&E asset life. Negative energy balances were calculated for both flowsheets, but the AP flowsheet required the least additional energy demand, as 56 % was offset by on-site energy generation. The desludge frequency calculated for the AP was 2 years, reducing tankering visits to site from 240 for the conventional flowsheet to 10 for the AP over the 20 year period, providing significant savings in O&M costs and carbon emissions. Over the 20 year LCCA, the TF and AP flowsheets were very similar in costs, at £240,481 and £252,749, respectively. Interestingly, the commonly cited prohibitive factor of APs, the costs associated with extended land requirements, were found to be negligible for the case of rural bare land sites. With rising energy and carbon prices putting pressure on the water sector to find alternative solutions for WWT in decentralised areas, APs may present a new approach to reduce the current burden of maintenance and sludge handling requirements.