How we can prevent raw sewage polluting our rivers

written by Soma Mukherjee

Soma Mukherjee (MSc, Environmental Management at Bath Spa) Interned at HBBE between June and September 2021. The following is an abridged extract from the project carried out with the HBBE.

The spoiling and pollution of our freshwater environment not only destroys the natural aquatic ecosystem and depletes biodiversity, but also poses a health threat to wild swimmers and those engaged in water sports. This blog gives a brief overview of why and how this pollution is worsening, as well as possible solutions with news of exciting novel research at HBBE (Hub of Biotechnology of the Built Environment, a joint initiative of the Universities of Newcastle and Northumberland and funded by Research England) that would allow us to treat sewage ‘in house’.

Introduction 

Our sewage system in Britain was designed in Victorian times and, as it incorporates combined sewer outflows (CSOs), allows raw sewage to overflow into rivers, particularly in stormy conditions. This system safeguards buildings from flooding and from sewage backing up into streets and homes.

 However, the sewage being discharged into rivers has reached alarming proportions in recent years. For example, the Environment Agency-published figures for the year 2020, show that sewage was deposited into rivers in England more than 400,000 times, so that human waste flowed into rivers and waterways for longer than three million hours. Indeed, although there is much public outcry and political will to legally prevent water companies from further sewage deposition, the recent inland waters bill failed in the UK parliament (see references below). The failure was attributed to concerns that the soaring costs of updating our antiquated sewer system might bankrupt many of the water companies, or that taxpayers would have to pay these huge sums instead. This highlights both the urgency as well as the complexity of finding solutions to the ongoing pollution of our waterways.

How sewage destroys aquatic life

When raw sewage flows into a river, it increases the amounts of nutrients (such as nitrogen and phosphorus) in the water, by a process termed eutrophication. The increased nutrients in the water result in an increase in algal blooms, and the microbes that feed on them use up oxygen, a process that severely depletes the amounts of dissolved oxygen in the water.

 This results in ‘dead zones’ arising within the water body, which are areas that lack sufficient oxygen to support most aquatic wildlife. Algal blooms also produce substances that are toxic to both humans and wildlife.

Why sewage in rivers is increasing

Sewage being deposited into water bodies is increasing due to climate-change evoked storms. This elevated frequency of higher intensity storms has resulted in the sewer system exceeding capacity and thus channeling wastewater via the combined sewer overflow pipes, and into rivers.

Also, as the numbers of buildings and road networks continue to expand, the proportion of the ground surface being impermeable to water increases. This results in flooding and the water being drained through the sewer system rather than the natural infiltration of rain through the ground to the water table.

The effect is further exacerbated by population growth, generating an ever-growing burden of sewage flowing through the antiquated sewer system. 

One possible solution to this may be treating human effluent within the house, using for example, composting or anaerobic digestion (AD) technology, at the household level. AD is an inexpensive technology that generates energy from waste and has been utilized, mostly at a domestic and smaller-scale level, in developing countries, such as China and India, where the products (carbon dioxide and methane) are used for cooking and lighting in the home. The other byproduct generated by an AD is digestate slurry, a soil supplement high in nutrients, that may be used as compost.

 If this can be accomplished, new houses may then have the facility to sanitize the waste of all its inhabitants without the need to add any further pressure to the sewer system. 

The fact is that AD can be scaled up as municipal waste treatment (in the developed world) and in farms (which have medium sized digesters) but AD technology at the household level has yet to be developed in a way that is feasible for implementation in wealthy nations. However, it is a renewable and clean technology, that not only lessens greenhouse gas emission of methane into the atmosphere, but is a way of recycling waste, and thus reducing pollution to air as well as to the water body.

Household AD prototype at HBBE 

New research, funded by Research England and based at HBBE (Hub of Biotechnology in the Built Environment), a collaboration between the Newcastle and Northumberland Universities, is developing a prototype system combining a toilet that funnels the sewage into a small AD treatment plant inside the home. The AD plant will take up approximately 5 m³ of space and may be housed in a cupboard or under the bathroom.The toilet (made by Laufen) channels the urine to generate power by using microbes (with the microbial fuel cells or MFCs), while the solid waste is processed by anaerobic digestion to generate biogas (that can be used as renewable fuel for the home), and digestate slurry (rich in nutrients and can be used as soil improver/compost). This could generate 3 kilowatt hours of electricity per day, which would significantly supplement the household’s energy use with renewable energy (the average UK household uses approximately 8 kwh/day).

The research aims to develop the efficiency of the process and genetically modify the microorganisms to further optimize the yield of biogas fuel, as well as to modify the system for ease of operation within the house.

Part of this initiative includes the OME, which is an experimental house, built within the campus of Newcastle University. 

Conclusion

AD technology must be adapted to operate reliably and efficiently at the level of the developed nation (such as the UK) family home. If this can be achieved successfully, it will increase the energy self-sufficiency of the household, sanitize waste, save water, mitigate sewage stormflow into rivers and lower GHGs.

Anyone wishing to find out more about these topics can go to the following links:

Sewage (Inland Waters) Bill – Parliamentary Bills – UK Parliament

MPs set to reject move to make water firms cut sewage discharges | Rivers | The Guardian

Tory MPs defend votes after uproar over sewage proposals – BBC News

Nature recovery for Thames, but river at high risk from sewage and climate change, report finds | Zoological Society of London (ZSL)