An unlikely topic of discussion?

Sludge disposal is probably not the most glamorous subject for debate. It is unlikely to be one of the first things that springs to mind for an after-dinner discussion. Think again. Recent shifts in the treatment and
disposal of sludge make it a shining example of how stakeholder pressure, and not legislation, is driving the water industry towards a more sustainable solution.
The means by which water companies dispose of waste sludge have changed significantly as a result of various pieces of legislation governing both the treatment and subsequent disposal of sludge.

With the UK responsible for almost 20% of the sludge produced in the EU, where total sludge production is estimated to rise to 10M tonnes a year by 2005, sludge disposal is by no means a small issue.

Over the past 20 years, the preferred routes for disposal have shifted from the unsustainable – dumping at sea and landfill – to more sustainable approaches. The most significant shift has been in the re-use of treated sludge as an agricultural fertiliser.

Legislation has closed the sea dumping option and an alternative has to be found for landfill, which was the ultimate destination of over 50% of sludge just ten years ago.

The government and many companies have stated their preferred route for disposal is currently to agricultural land – and this is where the after-dinner debate can really become interesting. The treatment and testing methods governing disposal, or more appropriately, recycling, of sludge on agricultural land are an excellent example of how stakeholder pressure, not legislation, is controlling the supply chain.

The conventional disposal routes of dumping at sea, landfill and incineration are all examples of a market that is driven by legislation. Meanwhile, the agricultural route is influenced by stakeholder pressure, in this case primarily the British Retail Consortium, with future legislation lagging well behind the market.
There is actually nothing new about using biosolids in agriculture – it has been done since the beginning of agriculture and, of course, there is legislation governing their application and use.

But as Peter Soulsby from Southern Water, which has pioneered many of the processes used for treatment and analysis, explains, the voluntary controls are tougher than the legal instruments: “Recycling biosolids is covered in the UK by the sludge regulations of 1989, supported by a code of practice.

“Going beyond this, the industry has developed the safe sludge matrix, which is a collaborative effort by Water UK and the British Retail Consortium, and incorporated hazardous analysis and critical control points (HACCP) or management into its processes. The industry and stakeholders are waiting for the review of regulations to incorporate the safe sludge matrix and the HACCP.”

Two standards of sludge are defined by the matrix – those that are conventionally treated and those undergoing enhanced treatment. The subsequent use is tightly controlled, both in terms of the crops to which it is applied and the harvest interval.

An interesting fact, possibly a good one for after-dinner discussion, is that biosolids actually only account for 2% of the total organic waste material that finds its way onto agricultural land.
A further 4% is industrial waste and the remaining 94% is animal manure and slurry – which is a lot of manure.

By establishing voluntary standards, the water industry has safeguarded a valuable disposal route, which is acceptable to stakeholders, particularly the British Retail Consortium. However, along with the safe sludge matrix comes more stringent testing requirements. In particular, the monitoring of faecal coliforms (specifically E.Coli) is an important step in determining the ultimate safety of the biosolids. Already well-established in drinking water, faecal coliform testing of sludge poses challenges for microbiologists, as Rob Fuller, the laboratory commercial team manager at Southern Water Scientific Services explains: “There are a number of differences between sampling sludge and drinking water for faecal coliforms. Most of the established techniques have been developed either for water or food samples. Unfortunately, sludge does not behave like either of these.”
“The main problem is that while water is an extremely homogenous fluid, sludge is not. This means the sampling protocols adopted are critical in order to obtain a representative sample.” Dr Fuller and his team of scientists recognised the need for even better sampling and monitoring of both E.Coli and salmonella. As a result, the company has recently invested in a much more advanced monitoring technique. This allows sampling to be undertaken without the need for the repetitive dilution that standard procedures require.

“The object of the exercise is to reduce dilution stages while ensuring sampling is entirely representative of the entire batch”, Fuller comments. There are also important health and safety issues for laboratories undertaking sludge sampling, especially if they are also carrying out drinking water sampling.

With HACCP ensuring critical control points are set throughout the production process, monitoring sludge quality is no longer simply an end-of-pipe procedure.
These measures, coupled with advanced E.Coli analysis of the type now being offered to the industry by Southern Water Scientific Services, will ensure recycling sludge to agriculture continues to be sustainable and, crucially, is carried out to the satisfaction of the British Retail Consortium, the Food Standards Agency and most importantly, the consumer. Southern
Water Scientific Services’ Coliform testing is available throughout the UK