Sewage Recycling - A Loop Almost Closed

I am pleased to present another interview this week. The subject of the interview (and of today's post) is humanure recycling for agriculture. But first, a bit of backstory.

Many writers on the subject of Peak Oil and collapse have discussed the challenges facing large-scale agriculture in a post-Peak world. A particular focus of their writing has been the steady depletion of soil nutrients and minerals resulting from our First World arrangements for growing, distributing and eating food, and disposing of the resulting waste. The whole system is unsustainable in the long run, since food that turns into human waste is now flushed down toilets and eventually into our oceans, taking vital soil minerals such as phosphorus with it. This requires the mining of inorganic phosphorus and combining it with other man-made components into artificial fertilizer in order to replenish depleted soils. But we are running out of the resources to continue this form of soil replenishment. Already there's talk of “Peak Phosphorus,” to name just one depleting resources.

Those who write about post-Peak agriculture have therefore said a lot about the need for individuals and communities not only to start growing their own food, but also to start recycling their own humanure. Many of these writers cite The Humanure Handbook by Joseph Jenkins (an excellent book by the way; I have a copy on my bookshelf). Jenkins outlines many steps that go into safe humanure composting for agricultural use, as well as outlining the dangers and environmental hazards that occur because of the improper disposal of human waste. However, his is an individual approach, and his composting methods are designed to be applied by individuals and households. This poses no problems as long as individuals and households are educated in proper methods and don't deviate from those methods. But people will be people, and in this fallen world, that means that some people are bound to mess a thing up, even if that thing is simple. I've met a few humanure composters, and at least one of them is doing it flat-out wrong. This can lead to ground water pollution and the danger of disease if carried far enough.

The other issue I have with the individual approach is that it assumes that any existing societal unit larger than the individual or small household is likely to be clueless about Peak Oil, peak pesources, adapting to a post-Peak world, or living with the reality of “the well run dry.” “Therefore it's up to us to start from scratch in preparing and adapting,” many writers would say. There's a lot of evidence for that opinion, especially when one looks at the Federal government and at many State governments. Lately, however, I've come to think that it's not entirely true that the members and leaders of larger societal units are utterly clueless about the issues of post-Peak adaptation. Sometimes within existing local structures it's possible to find people who are aware of resource depletion and who are already creating alternative means for people to get their needs met in a post-Peak world. I wanted to see if there were people within the Portland city government who understood the issues regarding humanure, sewage treatment infrastructure and budget constraints, and the problem of recycling nutrients back into agriculture.

So it was that I recently found myself at the Columbia Boulevard Wastewater Treatment Plant for an interview with Greg Charr, the Biosolids, Residuals and Reuse Program Manager. Before our actual interview, I met Mike, one of the senior plant operators, who took me on a tour of the plant. We spent a lot of time underground, beneath massive concrete roofs that comprised the undersides of huge tanks holding thousands upon thousands of gallons of water. I shot some video, which may or may not get posted one of these days. Mike explained how most municipal wastewater treatment plants worldwide have three stages of treatment: primary, secondary and tertiary. He then explained how the Columbia plant differed from some other plants in that its processes have been optimized to produce biosolids as a final product.

The interesting thing about these biosolids is that they are not the same as sewage sludge. Rather, they have been treated to such an extent that they are certified by the U.S. Environmental Protection Agency as safe for use in large-scale agriculture. Mike also pointed out the composter at the Columbia plant, and mentioned that it had been in use for many years before being shut down due to budgetary reasons. And Mike explained the working of the digesters at the Columbia plant and the challenges of maintaining digester chemistry and biology. The digesters at the Columbia plant produce enough methane gas to generate 1.7 megawatts of power at the plant (the plant uses a bit over 4 megawatts), and they also sell gas to local industries.

Greg Charr explained the EPA restrictions and certifications required for labeling the output of a sewage plant as a “biosolid” suitable for use in agriculture. The EPA has three categories of biosolids: Class B, Class A and Exceptional Quality (EQ). Greg discussed Class B and Class A biosolids, and talked about how biosolids quality has increased over the last 20 years. At present, the biosolids produced by the City of Portland are not significantly contaminated by heavy metals. As far as residual pharmaceutical chemicals, Greg mentioned studies done by several universities that showed no significant danger from residual pharmaceutical chemicals in biosolids, due to the degradation of these chemicals by sunlight as well as absorption by soil particles.

The City's wastewater treatment plants only produce Class B biosolids at present. This is a problem, as the EPA allowable uses for Class B solids are limited. The Oregon Department of Environmental Quality (DEQ) also has restrictions on the use of Class B solids. Therefore these are not a practical fertilizer for home gardeners and small-scale urban farmers. Greg further explained the budget constraints that resulted in shutting down the composter at the Columbia plant. Composted humanure qualifies as a Class A biosolid, suitable for direct use in gardening and urban farming. But the City was not able to produce compost in a way that covered operating costs of their composter. The Class B biosolids produced by the Portland treatment plants must be trucked to eastern Oregon for use in dryland farming. Eastern Oregon's semiarid climate helps the biosolids to break down without contributing to pollution of stormwater runoff into rivers.

At the end of the interview, I asked several further questions related to composting. It turns out that there are several companies in the U.S. who are already doing sewage composting on a large scale. (One of those companies, Synagro, has been in the news lately due to a corruption scandal involving the City of Detroit's sewage treatment.) I have a hunch (although I haven't researched it) that it may be hard for large companies to make a large profit from sewage composting, and that this is something that might be better suited to smaller outfits using low-tech methods. At present, it is possible to buy commercially produced sewage compost in the U.S., although it's likely to be a bit expensive.

I mentioned the City's combination of both high tech (Big Pipe) and low tech (eco-roofs) approach to managing stormwater, and asked whether the City was looking into low-tech methods of dealing with human waste, such as teaching people home-scale composting. Greg stated that this is not currently being considered by the City – but I hope my question will provoke some thought! The organized deployment of low-tech approaches will be increasingly important in the years ahead, as cities and counties continue to face shrinking budgets and as it becomes harder to maintain wastewater infrastructure during a time of economic decline.

A podcast of the interview can be found at the Internet Archive at this address: Sewage Recycling – A Loop Almost Closed. Also attached is a PowerPoint presentation which Greg provided, covering the main points of his talk, as well as links to some supplementary reading material, as listed below:

• “Photodegradation of the Endocrine-Disrupting Chemical 4-Nonylphenol in Biosolids Applied to Soil”, Kang Xiaa and Chang Yoon Jeong, Universities of Georgia and Louisiana, September 2003.

• “Frequently Asked Questions | Biosolids | Wastewater Management”, United States Environmental Protection Agency.

• “Class 'A' - Exceptional Quality Biosolids”, Portage County Water Resources, Portage County, Ohio.

• “Biosolids Technology Fact Sheet”, United States Environmental Protection Agency.

• “SCHWING Bioset - Products - Bioset Process - Class A Biosolids”, Schwing Bioset Incorporated. (I include this link as an example of a relatively high-tech process that may not be readily available very far into the future.)

My visit to the Columbia plant was profitable, and I appreciated the opportunity to talk with knowledgeable people about these issues.

City of Portland Biosolids Presentation

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