Last Friday at The Institute one of my colleagues in Engineering hosted a mini-symposium on sewage sludge: how to process, de-toxify, transport and process the stuff. The event was sponsored by Veolia the French water, waste and energy conglomerate. Sponsorship meant free food; so I was on it like bird shit on a car bonnet. There was a helluva lot of food but really not many people "It's a bit of a niche interest, processed human shit, isn't it", I suggested to the bloke behind me in the auditorium. After I'd grazed for 40 minutes on goujons and chipolatas while chatting to my room-mates, we went in to the first talk . . . by the Sludge Engineer for Irish Water. She had come up from Cork to talk to the very select audience. Even with people who were in the field, she seemed to have an uphill struggle against the perception of sewage sludge as anything other than a toxic liability.
It sounds like it should be a marketable product: rich in phosphates and nitrates, suitable as a soil bulker and conditioner. At least you should be able to give it away for free. My neighbour-above has been [twice] happy to take tonnes of the stuff from the Veolia waste-water treatment plant WWTP in Kilkenny to spread on his fields. Both times delivery-failures up our steep, unpaved dirt-track access has been a disaster for us: one spill and one stuck trailer this summer. It is indicative of the public relations market in sludge that in the first incident the sludge was free but the farmer paid the haulage. 5 years later Veolia is prepared to pay the haulage as well just to get rid of the stuff. WWTP currently generate 230,000 squidgy tonnes = 60,000 tds [tonnes dry solid] of sludge a year and there really aren't enough people or businesses to take the stuff so some of it gets diverted to landfill.
Stats. There are 500,000 private septic system across the rural Ireland. 60% [N = 376] of Irish WWTPs deal with the sewage from < 500 people. Only 11 plants treat for more than 100,000 p.e. [person equivalents]. Bring back the night-soil men! If we all shit in a bucket we'd waste a lot less water and be more mindful of cleaning up behind ourselves rather than flushing it all away for Nanny State to deal with.
Sewage sludge has a peculiar, particular and persistent smell. That alone makes people think it is a bit fishy. Then there is accumulating data that, apart from NO3- and PO4+, sludge is loaded with cadmium, nickel, microplastics, anti-microbial resistance AMR compounds, unprocessed pharmaceutical residues and, ominously titled, emerging contaminants. aka unknown horrors. The trouble is that ordinary people are as thick as shit in the use of the flush-toilet: wet-wipes and sanitary towels are the least of it. IF the privatised trash collectors start to charge by weight ANDIF people continue to rebel against paying water charges THEN the WWTPs are going to see pizza-crusts, plastic bags, potato peel and holed socks appear for processing.
One thing that emerged from the seminar is that Irish Water's expert on sludge processing was largely at sea when it came to a deep knowledge of the problems associated with its handling and treatment. In the audience were 3 or 4 representatives from the local authority who were responsible for five pilot sewage processing projects involving reed beds. We were presented with an executive summary for where these plants were set up and how they worked. In the post-talk Q&A an old chap on the other side of the room asked why they were using Phragmites australis the common reed and why it had to be imported from Poland . . . Phragmites only grows for six months in every year; there were at least 30 other reed species which grew year-round in the Irish climate. From the public employees, there was no answer at all, let alone a coherent response to this question. The old chap then asked a supplementary question about the complex set of 'aeration' pipe work in the reed-bed: "You are aware that Phragmites is quite content to grow in seriously anaerobic conditions where it is quite capable to finding enough oxygen from the atmosphere?". Pfffffff collapse of stout government-employee parties. Now I'm sure it's more complicated than that, and Irish Water had shelled out wodges of wonga to their own consultants in the design of their reed-beds; but the optics were terrible.
Sewage sludge really needs a public relations campaign to convince us that it is an asset and not a liability. I didn't have the chance to suggest that all Irish Water employees who are pulling in more than €60,000 a year should be obliged to spread at least 60kg of sewage sludge on their gardens [kg pro-rata for higher salaries] - because it is so good for the roses. It is nearly 30 years since the daughter of UK's Minister of Agriculture refused to eat a BSE contaminated beefburger.