Through the unit on waste water treatment, we learned that there are two main challenges involved in waste water management. These are sanitation and recovery. All waste water facilities need to be concerned about pathogens getting into the water supply and they also need to worry about contaminants such as oil and gas. When they treat non-hazardous water, they run everything through giant tanks that they call digesters. The Fond du Lac waste water treatment plant runs its water through a series of four digesters, two at a high temperature and two at a cooler temperature to help kill off all the bugs in the water. Treatment plants also have to use a lot of water to keep everything clean within the plant and they have to aerate the primary treatment tanks while the aerobic bacteria break down the ammonia and biologic elements within the water. From this process, they recover water, fertilizer, and methane gas. All of this takes a lot of energy.
Something different that the Fond du Lac treatment plant is doing is recycling its methane instead of wasting it. Methane is a by-product of the treatment process and is often flared off into the atmosphere or reduced to solid form and spread across the fields as fertilizer. However, Fond du Lac is siphoning off the methane, running it through different cleaners and then feeding it into an engine that’s connected to a generator. The generator creates electricity which is, in turn, fed back into the treatment plant to treat more water. On the tour of the plant, we learned that methane in its raw form coming out of the water treatment process still contains two elements, hydrogen sulfate (H2S) and something else which is a by-product of soaps and other cleansers used in personal care products. This second element is essentially a fine, abrasive dust which can damage the engine in the building but, once the methane is cleaned, the plant is able to produce about half of the energy it needs to operate. This is increased by their voluntarily processing water from nearby cheese factories which naturally has more methane within it. The engine and generator are able to produce about 400-450 kw.
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Since all landfill and waste water treatment plants produce methane as a natural by-product of the sanitation process, it is possible for this type of engine/generator combination to be put in place at other facilities. Where they might differ, though, is in the amount of energy they will produce. They are limited to a large extent by the type of waste they process. The Fond du Lac plant is fortunate enough to be in an area where there is a high level of methane content in the waste they process. They are also able to take advantage of the situation by offering to treat water from the cheese factories for free as a means of farming that waste for methane. Other treatment plants may not have access to such a rich supply. The average level of methane within the waste they process will determine whether it is actually feasible for other plants to consider this kind of approach. Since all treatment plants must have methane flares, though, it seems all could benefit at least to a small degree from such a change.
Understanding the enormous amount of energy and time involved in processing water makes it clear how much we need to focus on conserving as much water as we can. Relating these ideas back to the articles from last week, the droughts in the western part of the United States will only make the processing of water more difficult. They use a lot of water just to process water and the slower the flow through the plant, the longer it will take to clean everything through. Conserving water and properly treating water from the city to use in the farmlands might also help alleviate the problems being experienced in Mali as the wetlands are drying up from the diversion of water. Water is a much more important commodity than we usually think of it as being and we need to be more diligent in protecting it at every stage of its cycle.
- Davis-Foust, Shannon. ‘FdlWWTP final.’ Available https://www.youtube.com/watch?v=o1CtVCCS_NQ
