BIOHEAT: Husbanding biological heat to transform wastewater treatment

The world's population stands at 7.5 billion and the UN predicts this could rise to 11 billion by 2100 with increasing urbanisation [13]. The production of human wastes and wastewaters in an unavoidable consequence of life. Treating this so it can be safely released to the environment is of paramount importance to both human health and the ecosystems we depend on. Effective technologies exist which are able to treat the large volumes of wastewater produced in urban areas, but these have changed little in the last 100 years. Activated sludge is the most prevalent method used (by volume treated) but it is energy intensive, accounting for as much as 3% of electricity consumption in developed economies [15]. Furthermore 80% of the world's wastewater goes into receiving waters untreated [16]. This technology is expensive and unsustainable for some, but for large parts of the world is simple unaffordable.

A large proportion (roughly 50%) of the energetic costs in the activated sludge process comes from the need to bubble oxygen through the large tanks of sewage, such that the aerobic bacteria within these wastes can use the oxygen to digest the organic matter to carbon dioxide within the waste, making it safe to release to the environment. However there is energy contained within these organics in the wastewater. In activated sludge all this energy goes to the microorganisms, and we as engineers are unable to access it. Thus although effective, the activated sludge process uses substantial amounts of energy to get rid of the energy within the wastewater.

If we are to move to a more sustainable form of wastewater treatment, the aerobic activated sludge process need to be replaced by an anaerobic technology. Anaerobic technologies also use naturally occurring bacteria to digest waste, but here as oxygen is not present the bacteria must produce a different waste, methane in the case of classical anaerobic digestion, or electrons in the case of Bioelectrochemical digestion. In this scenario the bacteria take only some of the energy contained in the wastewater, and we as engineers can take the rest. Anaerobic digestion has also been around for 100 years and is used on many farm and industrial waste streams as well as on the sludge produced by wastewater treatment sites. However it is not effective at treating wastewaters which are dilute, and is not effective at the lower temperatures which are typical of the UK and other countries. Bioelectrochemical systems (BES) are a newly developing technology that use specialised bacteria to grow on an electrode and produce currents as they digest the wastes, essentially acting like a biological battery. BES technologies have been shown to work with dilute wastewaters and at low temperatures, however they are not energetically efficient, with up to 90% of the total input energy going missing.

Some of this energy will go to the bacteria as they metabolise, but some will be lost as heat. I hypothesise that when these bacteria live together attached to a surface in a biofilm, such as on an electrode, the heat generated is creating a localised warm environment allowing bacteria to survive and metabolise at low wastewater temperatures. Currently we do not know how much energy is going to heat, and nor do we have the ability to accurately quantify it. The aim of this grant is to develop a platform to make these critical measurements in order that we will then be able to engineer and husband the heat energy to transform wastewater treatment.

The scope of biological systems engineering is vast, from disposal and treatment of wastes and contaminants to production of chemicals and energy stores, even CO2 capture. A deeper understanding which will then allow for greater level of engineering and application will have a huge impact on society. With increased certainty of prediction, industry, government and ultimately 'the decision makers' are more likely to invest in these technologies. Using the water industry as an example the implementation of anaerobic technologies which allow for energy production rather than consumption will have far reaching impacts. At a global level it will reduce energy consumption and therefore consumption of fossil fuels, leading to the reduction of CO2 production impacting on global climate change. At a national level it will aid governments to meet targets for energy reduction and renewable energy production. At industry level it will reduce costs leading to increased investment in infrastructural change and economic strength. Most importantly at a local level it would lead to a reduction in the water bills for some, whilst for others may enable lifesaving sanitation to be implemented in areas where previously it has been unaffordable. These are the long term aspirations for developing a greater level of understanding of the energy transfers and microbial dynamics in biotechnologies, the new approach and the methods developed in this research will help move towards these goals.
As a more direct and immediate impact of this research, producing an energy balance for BES will help the commercial prospects for this technology. If we are able to confidently predict a percentage of the available substrate energy that is lost to heat, and the amount that is taken up by bacterial growth, we will then be able to more accurately determine how much energy should be available as an output of gas or electricity production. Actual calculations of these energy balances will be made using data from real wastewater treatment sites in order to make a realistic assessment of the financial viability of BES. This will be presented to Northumbrian Water to help with its strategy of investment in this technology, will also be reported to the water industry more widely through a publication in a trade magazine, and presented at an Institute of Water event.
EH will benefit from receiving this grant at this point during her career. Having arrived at academia late in life, and having had several career breaks, EH is now in a position of expanding her group and research portfolio with several PhD studentships already in place. Having her own independent research grant and RA supporting her will help towards her goal of becoming a world leading academic. EH will in turn support the career of the appointed RA giving them opportunities to develop skills in project management, presentations, paper and grant writing and networking.