All-in-one sustainability

New, highly mechanised wastewater treatment systems use more energy and produce more sludge. But LAS has a more sustainable answer

Sustainability is a word that is popping up with increasing frequency in wastewater treatment. Most water companies and many independent operators have a stated commitment to finding and developing sustainable solutions for treating municipal and industrial wastewater.

At first glance it seems odd, therefore, that energy usage for treating wastewater is rising year on year. One reason is tighter standards, and it seems we should accept there will always be an environmental cost to meeting higher water quality standards. Is this really the case though?

When faced with the need to upgrade or install new treatment systems, the overriding concern seems to be space availability on the proposed site. These space limitations have led to an increasing reliance on highly mechanised systems, which not surprisingly tend to be energy hungry.

Also, these systems tend to generate increased amounts of sludge. The energy cost of dewatering, tankering and disposing of this, although often left out of the treatment equation, still represents a real and significant financial cost to the operator.

Certainly, space constraints are often very real, and in these cases the operator’s choice is genuinely limited. Consider, though, the smaller rural site. The temptation might be to squeeze a high-tech upgrade into the available space but, by investing in a modest increase in space, you could achieve the desired improvement in treatment, cut energy input and eliminate all requirements in respect of sludge handling and disposal. Would this not be more sustainable?

Two villages in Norfolk are perhaps showing the way forward for these smaller communities by adopting new sewage treatment systems that meet current discharge requirements without producing sludge and with a minimal energy requirement.

Work has finished on an Aero-Fac upgrade for the village of West Newton on the Sandringham Estate. And work is under way on an Accel-o-Fac treatment system for the village of Holkham a few miles up the road. The Aero-Fac uses a mixture of wind energy and low-pressure diffused air to treat the sewage prior to the existing works, reducing the load on the original system. As well as coping with considerable variations in flow and load, the Aero-Fac process accepts surplus sludge from the existing works and digests it in-situ, eliminating the need for off-site disposal.

At Holkham, sludge handling and disposal are also eliminated with the installation of a new Accel-o-Fac system. This has even lower energy requirements than Aero-Fac, relying on wind energy supplemented by low-power electric back-up motors for calm weather.

At the Holkham plant, wind will provide most of the energy required for the cleansing process, and any sludge generated will be self-digested within the system. The process is odour free and requires minimal operator input. The use of aeration within the cells enables the required footprint to be significantly reduced, and prevents odours by ensuring that aerobic conditions are maintained throughout the depth of the water column.

Aero-Fac and Accel-o-Fac are modular processes that use aerated, facultative cells operating in series to achieve the desired level of treatment. Base levels of aeration are met using wind-powered aerators to minimise energy costs. And electrical energy is only required to meet load peaks and to maintain adequate aeration in still weather.

The method of aeration has been developed to avoid disturbance of settled solids, a key factor in successful facultative processing. This enables distinct aerobic, facultative and anaerobic zones to exist within each cell, permitting aerobic effluent treatment and both anaerobic and facultative sludge digestion to occur in a symbiotic ecosystem.

As well as low operating costs, CAPEX is generally significantly lower than alternative systems. No pre-screening is required and cells are usually formed using straightforward cut and fill techniques.

Recently, LAS has announced a new variant of the Aero-Fac system – the Aero-Fac Sludge Treatment System (STS). This is a standalone system for the on-site disposal of sludge produced by conventional WwTWs.

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