Plenary: Forty Years in the Black Stuff – Lessons Learnt

Evans, T., Tim Evans Environment



This paper is a retrospective of the last 40 years during which a lot has been learnt about the treatment and land application of biosolids and other organic resources. Starting with the statutory “Guidelines” (1976) through the Sludge Regs (1989), Quality Assurance (1989) and the Stakeholder Agreement (1998), controls have improved but the future depends on confidence and that is a house of cards. The stakeholder agreements were a milestone but do all parties apply their spirit all of the time? Is CATNAP (Cheapest Available Technology Narrowly Avoiding Prosecution) still a prevalent mentality? We have done a lot of science and have a good understanding of the risks and benefits and fate and behaviour of the constituents of biosolids and other organic resources. Phosphate has emerged as a prime sustainability criterion. We are exceeding the earth system boundary for phosphate by 5-times and for fixed reactive nitrogen by 6-times; this could be an opportunity. New treatment processes have been developed; some have disappeared again whilst others have proved their worth. The adage, buy cheap, buy twice, has been proved time and again. HACCP could have been a boon but has the lesson of “failure mode analysis” really been learnt? If something can go wrong it probably will. When the Engineer’s Representative was asked (nearly 40 years ago) how much the first big London sludge to land contract was going to cost he replied “it will cost what it costs to do it right”. We still brought the contract in on budget. Land application has a future if we remember the past and learn from it and if we spend what it costs to do it right but if the house of cards collapses, the alternative will be very much more expensive.

Keywords: branding; confidence; field trials; ground truth; HACCP; market research; odour; quality assurance; rheology; recovery; recycling; selling; stakeholders


Soil Science was a wonderful grounding for a career in biosolids. My research progressed from the reasons phosphate availability is low in strongly weathered soils from Brazil, which are chemically relatively simple to the interfacial electrochemistry of synthetic hydrous iron oxide, an even simpler model system. The black stuff was a whole lot more complicated but the principles of Soil Science applied and helped explain what was happening.

I joined Thames Water Authority, Metropolitan Public Health Division (MPHD) in November 1975; it was a time of transition. The largest of the sludge-to-land works was Perry Oaks, the sludge treatment works for Mogden (2 million p.e.). It occupied the space between the runways at the western end of Heathrow Airport (Figure 1). At that time lagoon-thickened liquid digested sludge was hauled to fields during an intensive summer campaign in sealed 8-wheel tippers that applied it directly about 20 cm deep; apparently this was a reduction on earlier practise.

Lagoons were operated on fill-settledecant-refill over a cycle of at least 6 years and there was a 6-month locked-off final settlement before emptying was allowed to commence.

The farming was mainly vegetables for the London market. The soil was deep loamtextured brickearth over gravel. Remarkably the only lasting damage was deep compaction from the massive axel loadings.

No adverse health effects were found amongst farm families that ate produce from their farms (Sherlock, 1982) but other research had raised concerns about heavy metal accumulation in soils and the effects it could have on plant growth (Chumbley, 1971). The experimental design was flawed but set in train development of “The Guidelines” (DoE, 1976), the forerunner of the sludge directive (CEC, 1986) and regulations (Anon, 1989).

The question facing MPHD was “would The Guidelines spell the end of London’s land application programme or could it adapt to them?

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