Slowly the "debate" we have been having on "biosolids", mostly played out in the media (churning) has been moving from what was a scientific environmental discussion into an absurd hysteria driven emotional miasma of illogic.
Let's set a few things straight here.
1. The best place, with no doubt whatsoever, to direct treated sewage, both liquid and solids types of waste, is back on to the land from which the nutrients in the waste originally came.
2. It is not just possible, but quite easy to treat sewage sludge so that it is safe for use on agricultural lands. This happens now all over the world, and is already common in Nova Scotia.
3. There are some sewage sludges that are probably not suitable for use for agricultural purposes because the sludge is the residual from more than simple domestic sewage (poop) and includes some industrial waste streams that contain heavy metals.
4. Not all sanitary sewage contains industrial waste. Parts of Halifax only produce domestic sewage, or organic waste that can be safely treated to return to replace nutrients stripped from that land by food or forestry production.
5. We do not have very much topsoil in Nova Scotia.
6. Anyone who eats rice eats food grown directly in untreated sewage that is probably from a third world country.
7. In case you've heard otherwise, the solution to pollution IS dilution, IF you can achieve a suitable level of dilution.
Let's take a more careful look at things. The real culprit in this story is the prehistoric (OK, Roman era) gravity sewage collection systems we have been saddled with, and continue to be subjected to by the engineering community and bureaucratic status quo. We have become addicted to these systems, allowing them to grow to unreasonable size, collecting waste from huge tracts of land, to one or two focal points. I've always simply referred to this as tearing a hole in the fabric of the environment. We go to a lot of expense to move all of our small problems to one place where it then becomes one huge problem.
A gravity sewer does several things very poorly. It concentrates what are initially small amounts of heavy metals, and other undesirable elements to a level where they actually become toxic. I hate to use that word because it has been so abused by the media and even some scientists, but lets just say that too much pure water can be toxic. A large gravity sewer collection system has the unfortunate side effect of collecting all the bad things to one place, and in doing so, allowing the sewage from the places that generate most of the nasties to contaminate the sewage that is relatively benign. Can anyone argue that the sewage from Burnside Industrial Park would not be vastly different from that coming from Highfield Park, just across the 111?
The second thing large gravity sewers do is allow water that is not dirty to enter the sewage flow. This is because sooner or later, they all leak. In much of the older parts of Halifax and Dartmouth, our sewers are combined sewers, which means they also carry water that falls as rain and enters catchbasins, footing drains, roof drains and so on. During a rain storm, flow in these old pipes is mostly rainwater. Sometimes 20 or more times what is coming from toilets and sinks and dishwashers. This extra flow added to the large regional collection system causes several environmental and engineering problems. First, it means that the pipes have to be large enough to carry it. When we engineers design gravity sewers, we allow a very large portion of that pipe's capacity for future infiltration or inflow of what would otherwise be clean water. We assume that it will get in, because it does. Manholes, in particular, are a major culprit - I refer to them as water induction devices. This is probably the single largest source of water pollution in Nova Scotia - it happens constantly all day and all night - water that is clean to begin with, leaks into sanitary sewers and is immediately turned to sewage.
Second, this extra capacity is inherently wasteful because it does not always rain, so the large (more expensive) pipes can wait with only a small flow for a while, and are only fully used when it rains. There is capacity that might carry more sewage, but it is used for conveying stormwater when it has to.
When it does rain, we see yet another major problem. If we try to treat what comes out of the end of pipe, we are confronted with a wastewater that does not exhibit the ideal characteristics for biological treatment. Ideally, in a typical traditional wastewater treatment facility, the process works best when the inflow is relatively constant, the temperature is higher, and the organic strength of the sewage is concentrated. These three parameters allow the biology we cultivate in a treatment plant to live and breed at a high rate, consuming all that nutrient our more inefficient digestive processes could not. But when we allow water to enter the collection system, we get three effects that are the opposite of what we want. The flow becomes highly variable - the rain causes peak flows which decrease the time sewage can stay in a treatment facility; the extra water is almost always cold, which lowers the overall sewage temperature and slows the biology working in the sewage treatment plant; and the extra water dilutes the waste stream, making it harder for the bacteria we want to be living in the treatment plant to find food. When it rains, it's as if those good bacteria we want to work for us are being abused - they are given less time to do the job, it is cold and they are slowed down by that, and it is harder to find the food to eat.
Finally, when we try to separate out solids so that they can be composted and otherwise treated for return to the soils from which they were initially taken, all that extra water makes it a very much more difficult task to do.
Large collection systems are a mistake. But we have them because we have always had a reflex reaction to the sewage we generate. Nova Scotians are fixated on flushing all our poop to the ocean, or to some bit of natural water somewhere. We are so tunnel visioned in this regard that we continue to build new outfalls to our lakes and streams and bays and estuaries, even when a less expensive option for returning the treated effluent to the land exists (read about drip irrigation dispersal of treated sewage effluent). Our history is terrible when we look back at the sewage systems operating in Nova Scotia today, from an overall environmental view. Why is sewage that is generated out by Kearney Lake being dumped into Halifax Harbour, miles away? This when the community generating that waste stream brings in treated water to irrigate its parks, and fertilizer (some of it from human waste in Milwaukee) to keep them green?
Why do we go to all the trouble and expense to create a huge concentrated point loading on the environment in the harbour, when the initial dilution of the pollution was not nearly so bad, and, close to the place where it was generated, comparatively simple to treat to tertiary levels, as compared to the basic screening and semi-digestion now practiced by our already out of date treatment plants? Why? The answer to that, when I asked back in 1992 was "Because that's the way we've always done it." Is that good enough for you?
Back to the sludge (I dislike the term biosolids, as it is not specific enough) from treated sewage. These large collection systems guarantee that people's objections to the reliability of the quality of the sludge produced from the waste at the end of these large collection areas will be valid. Heavy metals are fine in low concentrations - they exist in nature in low concentrations. In fact some metals exist in our native soils in fairly high concentrations (copper in the soils in Halifax, for instance is usually above CCME flagging levels, naturally). But when we go to the trouble to bring all the bad stuff to one place, then filter it all out from the water, concentrating it even more, we create a new material that may have more than is safe for use on crops we plan on eating.
So why don't we treat our sewage in smaller batches, closer to where the waste is generated, "at source" so to speak, where we can identify what sub-sections of our community generate solids that are safe, and can be safely used, while making sure that other waste streams are not included in that dispersal path?
If we used some careful public health engineering (by the way, Nova Scotia has no Public Health Engineer - the position was eliminated in a government restructuring back in the 90's) we could achieve a safe and secure supply of sewage sludge that could be treated to produce a composted land amendment or fertilizer that was safe from industrial contamination. Instead, we try to rely on diluting the industrial wastes back into our domestic wastes, with no reliable way of knowing on which day there is too much industrial contamination happening.
Back when the Harbour Cleanup was being proposed, I was one of a few people advocating for a solution based on a distributed form of sewage treatment. My point was that if the Harbour had not gotten dirty all at one time, it need not be cleaned up in an instant either. We could address the sewage treatment one community, one neighbourhood at a time. Treating the sewage before the massive inflow from rainfall and the contamination for industrial sources complicated the problem to the point where we could never afford to ever do tertiary treatment. All that was needed were treatment plant solutions that a community could accept as suitable in scale and nuisance, to host in their neighbourhood. That could take the form of underground/basement Sequencing Batch Reactors, community greenhouse based Solar Aquatics™ systems, or anything else that modern technology presented us with. Once that neighbourhood was served by a tertiary treatment plant, it would no longer be a part of the problem - the STP could simply discharge into the nearest major trunk sewer, which was probably originally a brook, making it that much cleaner, and the harbour subsequently that much cleaner as a result.
This approach had other advantages over the mega project that Halifax was hurtling towards. It was predicated on the idea that it did not all have to happen at one time. So the project might be funded out of an annual capital works budget, not some mega borrowing that we will owe money on forever. And the work could be designed and built by local engineering and construction firms, not by huge multinational corporations, meaning that we could create a centre of excellence in small to medium scale urban sewage treatment here in Halifax. Perhaps the best thing was that we could go out and solve the easy problems first - cherry-pick the places where the sewage was least dilute, where a location for a STP was available, and just clean that up. But do it so that 99% of the sewage was treated, as opposed to the +/- 40% we have now. We only really need to treat half the sewage going to our harbour to tertiary levels to remove the same amount of pollution as is now being done by treating it all to 40% removal! And the tough parts? Maybe by the time we had gotten all the easy parts done, a new technology will have been developed that can handle those (and this appears to be on the horizon now, with advances in microfiltration).
At the time, the absurd criticism we got from the old engineers in HRM was that there would be too many plants to operate - they would require too many people to run. This when NSPI runs all its hydro stations all over Nova Scotia from one control centre in Ragged Lake. And when the idea of a few good paying local jobs instead of cash sent to France for mega-project gear made some economic sense.
Of course, also at the same time, our rational arguments were hijacked by some well meaning, but ill informed eco-socialites who thought it a dreamy idea that a Solar Aquatics greenhouse system for Halifax would be just peachy! In fact they were advocating that the main treatment plant for all that dilute cold sewage in Halifax be treated in one greenhouse. I worked it out one day - the greenhouse would have to cover all of the Dockyards from Pier 9 to Purdy's Wharf to even have a chance at treating all the sewage in one place. But about 35 small to medium size treatment plants could do all of the metro area. This because the smaller plants would not be treated the huge peak flows that exist at the bottom of THE BIG PIPE. And we would not need any tunnels or outfalls - we'd just let the treated effluent flow out via the existing outfalls. Sure, a few could be consolidated or extended, but there would be no need to put it all in one place like we do now. And sooner or later, we'd have it all done. One bit at a time, the same way the harbour got dirty in the first place.
If this makes some sense to you, then you understand the concept of loading. See here for more on that if you don't. But this approach might have been impossible to get regulatory approval form because the regulators cannot apply common sense, they have to apply old standards based on the concentration of flow to the Harbour. They might not be able to look the other way when three pipes are say, 95% treated, but the one beside it isn't treated at all. Despite the net removal of pollutant being the same as what wold exist if they were all treated to a 75% removal. What they have accepted is a concentration based effluent discharge permit where it is possible that nothing is actually removed from the sewage, but enough water is added to it to dilute the concentration below some theoretical level. No one really cared about whether the harbour was being cleaned up, they cared about whether the stuff leaving one or two pipes was diluted enough to pass a concentration test, no matter how many thousand kilos of waste actually got to the harbour.
And that is where we now sit. We have a brand new, tunnelled at great expense, BIG PIPE that conveys all our little problems to three places where they each instantly become BIG PROBLEMS. So big in fact that we probably will never be able to remove the solids and nutrients in the sewage to even a secondary level of treatment, when it rains. But now the Federal Government is telling us we have to be more responsible, when we built a system that cannot really do any better than it does now.
The question remains as to whether it still might be of use to examine the distributed treatment approach again, instead of spending millions and millions of dollars to try to fix our current out of date treatment plants at their sites. Maybe there is a way that by strategically locating some small and medium size treatment plants we can reduce the loading to the plants we are now saddled with such that they, one day, might be convertible to processes that can actually reduce the loading on the Harbour. Time will tell, I suppose, but perhaps the first thing we should be doing is looking at where in that huge web of a collection system there might be places where the sludge collected could be safe for use in agriculture. And that location might be where we could look at both extracting that resource, and reducing the load on the central big old style STP's so that they might actually do something beside pass dilute sewage when it rains.
The best thing we can do now, though, because it costs so little, is to start looking at our older residential areas and seeing where we can get more stormwater to soak into the ground, or be used by trees, grass and other plants. Every bit of water we keep out of the pipes means less flow to the treatment plants, and gives them more of a chance to do the meagre job they can do. Rain barrels, tree wells that connect to gutters, snow piled on grass or earth instead of asphalt, dry ponds that fill up and hold water until it soaks in or evaporates, roof drains spun off to back yards instead of into storm drains, permeable paving, and anything that allows water to soak into the ground. These will all pay back continually in terms of helping the infrastructure we do have, whether ill conceived or not, perform as best it can for us, and for our environment.
