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article imageOp-Ed: Poo Power—DiY waste-to-energy and water conservation

By Victoria N. Alexander     Apr 9, 2015 in Environment
Home biogas reactors, used throughout China and India, turn human waste into energy, conserve water, and stop fresh water pollution. Why don’t we have these systems in the U.S.?
While California and Texas are drying up, residents of these states continue to use 1.25 gallons of fresh drinking water to flush their poop away. Regulations requiring low-flow toilets don't help enough because toilet design is not really the problem. The problem is with our approach to wastewater treatment in general.
map showing drought area increase 2013-2014
map showing drought area increase 2013-2014
Drought Monitor
Both centralized and decentralized conventional systems are in every way ill-conceived, expensive, environmentally hazardous, and a danger to public health. The problems start at the source, where waste toilet water is combined with wastewater from sinks, bathtubs and washing machines. From there the poop problem is kicked downstream to treatment centers where costly de-watering, chemical treatments and filtering take place, pollution is inevitable, and efficient recycling of any purified water pretty much impossible.
Designed to replace conventional septic systems, home biogas reactors are small on-site waste systems that use a process called anaerobic digestion to turn waste into methane gas and fertilizer. Reactors are simple and, properly installed, they are safe, clean and do not emit odors. These systems completely rethink how we deal with our waste and use our fresh water.
First, the amount of water going into the biogas reactor must be limited. These systems need water, but not too much. The blackwater from the toilets must be separated from the greywater from other drains. Water that is saved from contamination with human excreta can be recycled. It is not economically feasible to try to reclaim water for use after it has been mixed with blackwater, and this is why source separation is key to sustainable wastewater management.
Recycling greywater
Greywater can be minimally treated and filtered on-site with commercially available home systems and then reused to flush toilets or to water non-edible landscaping. Alternatively, greywater can be treated using constructed mini-marshes and potted grasses, as with John Todd’s award-winning Eco-Machine designs. Reclaiming greywater can reduce household water use 30 to 50 percent.
Recycling greywater has become absolutely necessary in drought prone areas. It’s also necessary to keep greywater out of the waste stream in wet areas where too much water in a septic tank can make the system fail, resulting in pollution and health hazards.
A typical small town wastewater problem
I first learned about on-site anaerobic digester systems about a year ago when I was asked to join my town’s wastewater committee. Like many small rural towns in America, we have a serious wastewater problem. On the one hand, most of the homes and businesses are too spread out to make a centralized system cost effective. On the other hand, the business, homes and apartments in the center of town are too close together to fit septic systems with adequate leach fields. In consequence, business development in town is discouraged, the town cannot generate as much tax revenue as it could otherwise, and residents are taxed at a higher rate than they would be if there were a thriving town center. In addition, our town is situated in a beautiful valley with a very high water table, which demands expensive septic systems for all property owners, many of whom are struggling farmers or retirees with limited income. Too many septic systems are not maintained properly, and they leak into groundwater and pollute the streams.
The committee hired engineers and talked to the county wastewater authority and came up with a $4 million plan to provide a centralized wastewater system for about 130 businesses and residences near the town center. I did not support the project because I had done some research on how other countries were dealing with these issues in innovative ways. I learned about the importance of source separation of blackwater and greywater and the benefit of anaerobic digestion systems. The project was not approved, and I felt my town could consider itself fortunate that the centralized system was prohibitively expensive. We are actually in a great position to incrementally and voluntarily start switching to a kind of wastewater treatment that would be cheaper, safer, and better in so many ways.
How the biogas reactor works
A toilet connected to an anaerobic digestion system can be a regular low-flow flush toilet. It is not like a composting toilet that does not use water. Blackwater goes straight from the toilet into the biogas reactor where it is mixed with kitchen wastes (preferably macerated), and mulched yard clippings. (Partially composted farm animal manure, if available, is also a good feedstock.) The reactor is maintained at about 80-95 degrees Fahrenheit (27-35 degrees Celsius) by a solar collector. In these warm, watery, nutrient-rich conditions, micro-organisms called archaea thrive and break down the solid waste and release methane gas, i.e., natural gas, which is captured and stored. Many small scale models simply have an expandable rubber top that inflates when gas pressure builds up. All biogas tanks have pressure safety valves that prevent over inflation. A household with four members can produce enough biogas in this way to cook a meal or two each day or run a small heater.
Loowatt Biogas Unit
Loowatt Biogas Unit
After about 60 days, the waste has made its way though the system and becomes an earthy-smelling compost-like material called digestate, which can be used or sold as fertilizer for certain crops, such biodiesel crops, cotton, hemp, or any crop not intended for human consumption. There is no liquid discharge involved, no need for a leach field, no need for further treatment with toxic chemicals. This is a "closed-loop" waste treatment system, in which nothing goes to waste, everything is used, and the by-product is green energy. If it's not closed-loop, it is not sustainable.
Biogas around the world
Farmers all over the world use anaerobic digesters to process manure. Methane that would otherwise escape into the atmosphere from dairy, beef and pork farms, causing further global warming, is instead captured and used to supply power to local electrical grids, as noted by the American Biogas Council. I believe this is a good thing, despite criticism from some environmentalists who say that these systems simply encourage further industrial agriculture. As an organic farmer, I know that there is plenty of manure to be collected in the barn during the winter when the animals are in there eating hay and snow is covering the grass or when cows or goats are being milked.
Very few of these farm digesters process human waste. I only found one in all of New York state with a permit to do so. Instead the typical farmer has the sludge from the home septic tank drained periodically, and although it would be practical to mix it with the animal manure in the digester, it is not. Instead the septic management company takes the raw sewage away and sometimes disposes of it by spreading it on pastureland where it creates a health hazard for people living downstream. America is sometimes not very progressive in the way it deals with human waste compared to some other countries.
Source separated anaerobic digestion systems have been used by households and small communities for processing human waste in India since the mid-nineteenth century. Many millions of systems are now in use in China, India, Africa and South America because no other type of system comes close to addressing their significant problems with poverty, sanitation, fuel scarcity and water scarcity. Also now in Europe a number of small upscale communities are employing technically advanced source-separated, closed-loop cluster systems with on-site anaerobic digestion.
1 500 gallon unit for small farm
1,500 gallon unit for small farm
Sustainable Technologies Institute
In the U.S. numerous university research teams are designing and testing systems for use in cold and temperate climates. In Virginia, researchers at the Sustainable Technologies Institute have designed a 1,500 gallon system with a solar heater, sized for a small farm or community of a few homes. Insulated systems can be placed in an outbuilding or built in-ground to help conserve the heat. The digestion process does not stop at low temperatures, but it slows down considerably.
England has an extensive biogas program that is doing well and powering municipal buses; however, since the greywater and blackwater are not separated at the source, the efficiency of the system is limited. There are currently over 1,000 off-site anaerobic digestion systems in the U.S. based at centralized treatment facilities. The technology is improving and more and more systems are added every year, but here too these systems require expensive de-watering due to the practice of source combining. After separation, the sludge is sent to an enormous digester. Restaurant food waste and agricultural wastes are added in order to encourage the anaerobic organisms to do their thing.
As some researchers note, with large systems it can be more difficult to maintain the correct pH levels. In the end, the anaerobic digesters that are part of big centralized municipal wastewater systems are ineffective and expensive. Ideally, It would better to separate out the blackwater at the source and treat it in small decentralized digesters and let the greywater go to the existing centralized system for recycling.
Small scale home biogas
Hestia Biogas Unit
Hestia Biogas Unit
Although there are several commercially available biogas reactor systems available in the U.S. for about $4,000, none of them are marketed for human waste treatment. The Hestia biogas reactor is sold as a system to digest garden and kitchen wastes in order to produce gas for cooking or heating. But the anaerobic digestion process requires the addition of some water and archaea micro-organisms found abundantly in animal intestines and manure. If a family does not happen to have access to cow manure, they might want to connect a pipe directly from the toilet to the reactor.
Regulations governing the safe disposal of human wastes are certainly necessary. Unfortunately, household digesters are not approved for human waste disposal, even though the conventional septic system is, arguably, a much greater health hazard. Septic tanks often fail if not maintained regularly; they can leach effluent and sometimes raw sewage into groundwater.
Septic tanks are familiar technologies and so they continue to be used. If maintained and installed properly they are safe and perform well. But these are some pretty serious ifs, especially when they depend upon individual property owners having sufficient financial resources to properly maintain their systems. They can fail despite proper maintenance during periods of heavy rain. A source-separated biogas reactor may be a better and cheaper system, but trying to get local officials to approve new systems is a long and arduous process. If a system is not on the very short list of approved commercially available systems, a local water authority may not even consider it.
When I questioned the representative from our local authority, I found she had not heard of biogas reactors being used on-site for human waste in other parts of the world for over a hundred years. She did not think source separation of blackwater and greywater would be feasible because homeowners would not want to change their plumbing, even though in our area, all homes have basements and direct access to most of the pipes. I realize that most people don't like change, but if homeowners are given the choice between a centralized system with a permanent 8% tax hike or calling a plumber for a one-time upgrade to a system that will eventually pay for itself, with savings in water use and energy supply, they may choose the latter—if only the wastewater authority would allow them to.
Health issues, disease control
Anaerobic digestion is by far the preferred method for eliminating pathogens in human excreta, but it does not get rid of 100 percent of it. Centralized treatments centers add chlorine before releasing “cleaned” wastewater back into the environment, but even this doesn't eliminate all viruses and harmful bacteria. This is an intolerable situation were we to be faced with a serious epidemic in the U.S. With a source-separated system, a community can isolate infected waste streams and deal directly with the problem at the source. With the rise of antibiotic resistant bacteria, hospitals should certainly be treating their wastestreams separately from the rest of the population. Recall that last October, county officials in Georgia considered refusing to treat the sewer waste from Emory University hospital during its Ebola crisis.
Another health concern is the high levels of pharmaceuticals that are showing up in streams, lakes and reservoirs, according to the World Health Organization. There are not sufficient studies on the possible health effects of this situation. Because our current systems are not source-separated, these chemicals are finding their way into fresh water systems and into our drinking water.
I am writing this article in part to let my neighbors know about this alternative to conventional waste systems and to encourage them, and other people throughout the U.S. in similar situations, to begin to implement these designs. If your septic tank is failing and you are looking at a costly system replacement — or if you are building new and can design a sustainable wastewater system from the ground up — consider implementing a source separated design with a greywater recycling and a biogas unit. You may be able to get a permit for a sewage holding tank in your area, and a biogas unit may qualify legally as a holding tank, but emptying a biogas tank will not be a frequent or costly problem as it is with a conventional holding tank. Do your homework first. Follow the links in this article or read up more thoroughly by looking at this book, the bible of source-separated decentralized wastewater treatment. Learn all about the necessary safety precautions and get an wastewater expert to give you help and advice. I’m going to get into some trouble for saying this, but I think some things are too important to wait for government to do the right thing on its own.
Eventually all wastewater systems will have to meet the source-separated, closed-loop, waste-to-resource requirement. No society is truly sustainable unless 100 percent of its waste stream is recycled. Source separating blackwater and greywater may be difficult for property owners whose pipes are already connected in the walls—or in cement slabs, which is the case throughout drought-ridden Texas. Fortunately, there are economic incentives to get people to switch voluntarily to this truly sustainable wastewater management system.
Follow Victoria N. Alexander so you don’t miss an article in her DiY political change series. Alexander is the author of Locus Amoenus, a post-9/11 political-satire novel.
This opinion article was written by an independent writer. The opinions and views expressed herein are those of the author and are not necessarily intended to reflect those of
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