Maureen Ntege

As sustainable development takes centre stage for government, industry and regulatory bodies, the water industry is finding itself in an awkward position of having to comply with increasingly stringent standards, while keeping consumer prices low. Tighter effluent standards with the hope of protecting the receiving watercourses forces operators to resort to high technology solutions that require relatively large amounts of resources (energy, manpower and chemicals) for nitrogen and phosphorus removal , to eliminate any risk of regulatory non-compliance. These high levels of resource utilisation are associated with increased Green House Gas (GHG) emissions, wider environmental degradation and costs. These issues are particularly of concern to remotely sited small wastewater treatment systems where the application of high energy solutions maybe inappropriate.

This report assesses the technical capacity and sustainability impacts of a range of tertiary wastewater treatment technologies for small sewage works, from the low energy, land intensive solutions to high energy small footprint technologies. The technical assessment shows that the low technological solutions are good at resisting hydraulic, toxic and inflow variations and do not require chemicals. However due to their sensitivity to temperature, the systems fail to meet the stringent Total Nitrogen and Total Phosphorus standards of 15mg/l and 1 mg/l respectively as stipulated in the Urban Wastewater Treatment Directive (UWWTD). The sustainability assessment shows that though the low technological options do not meet the stringent standards, they score well on the sustainability front. The high technological options meet the standards at the expense of wider environmental degradation. Phosphorus removal by chemical precipitation is by far the cheapest means to achieving the stringent 1mg/l at small wastewater treatment sites, but comes at the expense of an increase in sludge volume, and associated sludge handling and disposal costs.

Should the status quo be maintained? Or should the ‘partnering’ approach between regulators and operators to setting consent standards be applied in a bid to making overall sustainability the key driver in technological choice assessment as the U.K Water Industry prepares to embrace the Water Framework Directive?