A professor from the Missouri University of Science and Technology claims to have developed a range of new methods for processing wastewater that could achieve a complete turnaround in energy consumption and result in a cleaner and purer final product.
One of the key new methods developed by Dr. Jianmin Wang, professor of civil, architectural and environmental engineering at Missouri S&T, is the counter-intuitive measure of making the environments in which waste-consuming microorganisms reside slightly more hostile for them.
Wastewater plants usually maintain an oxygen concentration of two milligrams per litre in order to sustain the microorganisms that are used to treat the wastewater by feeding upon its noxious contents.
Wang said this volume of oxygen is enough to make the microorganisms ”happy,” with conventional wisdom dictating than a lesser amount of oxygen would make it more difficult for them to flourish.
According to Wang, however, it may be of benefit to the purification process to subject the microorganisms to harsher conditions by reducing oxygen concentration levels. Wang believes a lower concentration of oxygen – perhaps 0.5 milligrams per litre, may leave the microorganisms disgruntled, but would also prolong their lives and prompt them to do a better job of purifying the wastewater.
“You can make them a little unhappy,” said Wang,” because bugs do not have a union.”
In addition to compelling the microorganisms to do a better job of chewing through impurities in wastewater, reducing oxygenation levels can significantly cut down on the energy consumed by aeration of the processing tanks.
According to Wang, these reduced oxygenation levels mean you can employ 30 per cent less energy for the aeration of wastewater tanks while achieving equivalent purification results.
The method is also so simple that it doesn’t even require the retrofitting of more complex or sophisticated equipment on pre-existing wastewater treatment facilities – it simply involves dialing down aeration amounts.
Another wastewater treatment process developed by Wang is capable of producing superior effluent quality by expunging organic pollutants as well as nitrogen and phosphorus nutrients.
The Alternating-Anaerobic-Oxic (A30) process achieves this without the use of chemicals, while employing 10 per cent less energy compared to the conventional pre-anoxic process. Wang claims his method results in far greater total nitrogen and phosphorous removal, resulting in effluent that contains just five milligrams of total nitrogen and 0.5 milligrams of total phosphorus per litre.
The widespread application of the process could make a major contribution to efforts to deal with the eutrophication of surface water around the world – a major problem for global supplies of potable water.
Eutrophication refers to the injection of excessive amounts of chemical nutrients such as nitrogen and phosphorus into an ecosystem. This has a highly adverse effect upon water quality by fostering the growth of algae blooms that deprive other aquatic flora and fauna of oxygen and produce toxins that render water undrinkable.
Wang has also devised means of converting wastewater sludge into biogas energy by means of a self-mixing anaerobic digester, which operates without the need for an external energy source.
Wang estimates the cumulative impact of his technologies could be a net energy gain of 10 per cent, as opposed to the 26 per cent net energy usage of the wastewater industry at present.
This remarkable turnaround in energy consumption alone could have major ramifications for the environment and carbon emissions, given that as much as 0.8 per cent of energy used in the US is for the treatment of wastewater.
One of the systems devised by Wang is also highly likely to be adaptable to retrofits of buildings, given that it is compact enough to be transported by vehicle. His small-scale deployable baffled bioreactor (dBBR) is currently being tested at the Naval Surface Warfare Center in Carderock, Maryland.
The unit has proven to be 88 per cent more energy efficient than army guidelines when used to purify municipal wastewater, resulting in high effluent quality with low biochemical oxygen demand and suspended solids.