Raising the septic standard
Septic tanks pose a major threat to the environment, according to Mike Norton, technical director of wastewater treatment plant manufacturer Klargester. Natasha Wiseman found out more about his concerns and why a new British Standard will help address the issues
"I calculated that if half the UK's septic tanks were only working at 50% efficiency, you've got the equivalent of 131.4Mm3 of septic effluent going into our groundwater every year," he says.
"I've tested septic tanks in the field and I've found unbelievably high results in some of them. We had one with a BOD concentration of 570mg/l. We couldn't believe it. In theory the influent should only be 300mg/l."
The UK has half a million septic tanks and Norton estimates that his company supplies over 7,000 of the 10,000 added to the count each year, yet he describes the technology as "an anachronism" and is pushing for the industry to replace them with more efficient packaged treatment plants.
Norton has been involved with British Standards Institute in the field of sewage treatment for fifteen years, and remains active, especially in developing the painstakingly slow European standards. December 2007 saw the publication of Part 2 of the small sewage treatment plant (STP) European standard series EN 12566 as a new British Standard.
BS 6297:2007 relates to effluent dispersal in the ground in soakaways and has only been issued as a technical report, rather than published a full standard, in Europe.
"We commissioned a team to write up Part 2 as a British Standard," Norton explains, "so that it is published in the UK and available worldwide. Alison Anderson, who works for me, chaired the group which penned that British Standard, that is BS 6297:2007." (Norton explains that BS 6297:1983 was simultaneously withdrawn because it was in conflict with the equivalent European standard EN12566 in all its seven parts.)
In the UK, explains Norton, both manufacturers and the regulators believe that the use of septic tanks is totally dependent on the secondary treatment that effluent from the septic tank receives in the soakaway.
"The new standard provides for secondary treatment in the ground, which offers the homeowner biological treatment of his sewage waste without consuming energy, so its carbon footprint is technically lower than a packaged treatment plant," he says. "The problem is that his septic tank only treats by trapping the solids and then you get anaerobic digestion that is probably only going to be 20-50% efficient ... it's totally dependent on its downstream soakaway to go to treatment.
"It's brilliant if it works, the problem is that the soakaway's got to be right in all respects. This BS 6297:2007 describes exactly how the ground should be assessed to ensure that it's suitable."
The new standard includes a percolation test. Holes are dug a meter into the ground to take readings. They are filled with water and monitored to decide whether the speed of dispersal is conducive to effective treatment - too fast or too slow means that treatment efficiency is compromised. For example, if the ground is clay, it is unlikely that a soakaway would be practicable.
Norton sees building and planning as central to the problem with septic tanks. "The people who make the decision to buy a septic tank or a treatment plant are not normally the people who are going to live in the property," he explains. "They are the builder or the developer and he is really looking for the cheapest, fastest solution. He is not going to buy a treatment plant unless he's forced to.
"Often, the gardens aren't big enough to provide enough soakaway, so they just put in what fits. And then there is another condition that the groundwater table needs to be at least 1m beneath the entry point coming out of the septic tank into the soakaway - and it needs to be a meter below that 365 days a year - it very often isn't.
"So the effluent from this tank, that's only been treated 20-50%, goes into the ground with probably too short a soakaway in the wrong ground and it gets to this place where it is flooded. It gets diluted into the groundwater. So what you've got is treatment by dilution - or would you like to call that pollution?" he warns. "Because that's what you get."
Norton is quick to challenge the short-sighted drive for carbon cutting energy efficiency at the expense of other forms of pollution - "green pollution" he calls it. In preference, he sees packaged treatment plants, which remove a healthier 95% of the pollution at the tank outlet, as a necessary replacement for septic tanks.
"Although septic tanks use no power, a treatment plant only uses between 40-60W, which is the same as a pretty modest light bulb," says Norton. "There are lots of innovations coming along.
We are at one with the regulator in our desire for low energy consumption."
Raising the standard
Given his enthusiasm for packaged treatment plants, it is not surprising that Norton sees Part 3 of EN12566, which covers PTPs, as the most significant part of the European standard. It includes rigorous testing of the biological and hydraulic performance of PTPs over a 38-week period.
Plants are underloaded, overloaded and generally stressed to measure how well they survive the different traumas they might encounter in situ. The test involves an up-front additional time-frame stabilisation period, typically of a month. In the end, the results are published.
"The laboratory has to declare the treatment efficiency in several different parameters: BOD removal, ammonia removal, suspended solids removal and so on. We have declared what the UK regulators will normally expect as minimum performance, and that is what we will call 20-30-20 and that is 20mg/l BOD, 30mg/l suspended solids and 20mg/l ammonia," explains Norton.
"That means you are looking for nominal treatment efficiencies in excess of 90%. Certainly on solids and BOD, the ammonia would be a lower number in terms of percentage.
"The standard does define the acceptable influent range of those parameters. If the influent that comes into the laboratory for treatment using all these test plants, because they'll be running 30 test plants at once all in parallel, exceeds or falls below the minimum loads, they have to declare and not use the data from that day's testing.
"These tests have to be carried out in a laboratory with restricted supervised access by the suppliers and they have to be carried out by a notified body," says Norton. "The publication of the reports doesn't define a pass mark, you have to declare your performance and that covers treatment efficiency, it also covers structural adequacy and the fact that the things don't leak.
"Those are basically the essential requirements and the essential requirements are a major aspect of the European standards under the Product Directive. Publication of the report and testing enable the manufacturer to place a CE mark on the product, giving the customers confidence. There is no alternative performance standard. That is the main deliverable that we have achieved in terms of European standards for small STPs," Norton concludes.
People on board
Norton is well-aware that technology is not the only barrier to introducing a new standard. "It's all very well having a standard," he says, "but you've got to have people subscribing to it, using it, recognising it, implementing it."
Recognising that these treatment plants are only as good as how much love and attention they receive, he helped set up a British Water accredited scheme for training and certificating service engineers in this sector, based on the Corgi scheme for gas servicing.
"Many years ago, the industry had a bad name because these treatment plants were bought and switched on and forgotten. If you do that, it's like a car: if you don't service it, it will break. And you don't want something that is treating domestic sewage, in your garden, breaking because you don't want to have an environmental health hazard in your home.
"When we sell someone a treatment plant, we don't want to just grab their money and run, we want to look after that plant for the rest of its life."