Pretreatment of blackwater improves the use of membranes for water treatment

Membrane distillation is a potential technology for non-sewered sanitation to achieve a high standard of treated wastewater. However, there have previously been issues with membrane distillation’s potential when it comes to concentrated blackwater. 

Treating concentrated blackwater with ultrafiltration before using membrane distillation has been shown to improve many factors of membrane distillation as a wastewater treatment method. Ultrafiltration removed large particulates from the blackwater, meaning that the membrane distillation permeability was raised to similar levels to that of just urine. This increase makes the membrane distillation water quality to acceptable standards for discharge or reuse.  

These findings show that membrane distillation can provide a robust means for concentrated blackwater treatment. As the energy required for ultrafiltration is primarily heat, this treatment can be delivered to areas with more fragile power networks, making it more accessible to the communities in need of safe, non-sewered sanitation options. 

Full article: Ultrafiltration pretreatment enhances membrane distillation flux, resilience and permeate quality during water recovery from concentrated blackwater (urine/faeces), Farhad Kamranvand et al, Separation and Purification Technology

Characterising properties and energy content of FOG waste at different catchment points

It is a well-established fact that fats, oils, and greases (FOG) cause several issues for sewer systems. They accumulate at various points in the catchment and lead to oily wastewater, floating masses, and hard deposits. Despite the detrimental effects, FOG has a high calorific content making it an ideal feedstock for energy recovery processes. However, the overall volume of each type of waste and their properties in relation to their collection point have not been researched thoroughly. This knowledge is needed to create a viable solution for FOG collection and energy recovery.

STREAMer Thomas Collin collected FOG waste from households, food service establishments (FSEs),  sewage pumping stations, sewers, and sewage treatment works. These samples were compared to sewage sludge in regards to organic content and energy potentials. FOG recovered at source (household and FSEs) was ‘cleaner’ and had a higher energy content. Once mixed with wastewater, the composition changed and lost some energy per unit mass. 

The results showed that around 94,730 tonnes a year of these materials could be recovered from Thames Water utilities catchment, which is one of the most populated in the UK. This could translate to 222 GWh per year as biogas, close to double what is already produced with sewage sludge digestion and covering 19% of the company’s energy requirements. 

Even though there are 6 million households in the catchment area, most of the FOG waste was produced by 48,000 FSEs - an estimated average of 79,810 tonnes per year compared to 14,920 tonnes per year from private households. As recovery from FSEs will be cheaper and easier if companies implement a collection system, this difference is of significant interest. Whilst feasibility of a collection scheme must still be considered, this is a big step in the right direction. 

Full article: Characterisation and energy assessment of fats, oils and greases (FOG) waste at catchment level, Thomas Collin, Rachel Cunningham, Bruce Jefferson, Raffaella Villa, Waste Management

Developing an environmental flow framework to assess small scale impoundment

Many rivers have had some form of modification to their natural flow for services such as water supply and hydropower. This is typically done by impoundment, which is the term for any structure that raises water levels, such as dams or weirs. As the demands for water supply and hydropower increase, it is hard to prevent them from being implemented. However, it is agreed by most that typical modified flows do not sufficiently cater to the needs of downstream ecosystems. As such, more must be done to understand their impacts and mitigate any issues. 

Ian Hough, a STREAM researcher, developed a novel, transferable framework to assess a small scale impoundment in North West England, using linked hydro-ecological modelling. The model employed flow velocity measurements and macroinvertebrate sampling data. Predictions of habitat quality were created using established ecological principles, such as the importance of flow heterogeneity (being nonuniform and diverse). The results were then used to design environmental flow regimes, aiming to improve ecological metrics whilst considering the conflicting water demands.

Based on historical flow records, implementing designer flows over 12 months showed increased peak species habitat qualities by 23-26%.  Characteristics such as flow heterogeneity were more natural, and 22% water was released from the impoundment. If these outcomes are validated experimentally, there is a great potential for further development and application of this method. The method could also be used in other sites of similar magnitude and geography, so the transferability of the model makes it even more useful if validated experimentally. This could result in fewer negative effects happening due to impoundment. 

Full article: Designing an environmental flow framework for impounded river systems through modelling of invertebrate habitat quality, Ian Hough, Philip Warren, James Shucksmith, Ecological Indicators

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Exploring how aquifer depletion could affect agriculture

Freshwater aquifers are one of our main sources of water. Aquifers are layers of rock that bear water underground, and fill up from rainwater and melting snow. Aquifers can flow out in streams, but more frequently have wells drilled into them to pull the water for drinking, as well as industrial and agricultural uses. Aquifers can dry up if we drain them faster than they are refilled.

Many major aquifers around the world are exploited unsustainably, even to the point of approaching environmentally unsafe drawdown limits in this century. Aquifer depletion tends to happen in regions that are important to crop production, so dried up aquifers pose a global food security threat.

STREAMer Sean Turner used the Global Change Assessment Model (GCAM) to investigate the response to severe constraints on global water resources, focusing on the land use and agriculture sectors. A scenario was created where many important aquifers became so depleted that further withdrawal was not possible. The results from that model were compared to a control model that had no constraints on water withdrawals. 

The results of this study show that groundwater depletion and the associated increase in water price increased two distinct responses from the agriculture sector: there was an expansion in rain fed agriculture, and irrigated crop production shifted towards regions with cheaper water resources. Water stressed regions with groundwater being depleted unsustainably were most affected by losses in crop production. Specifically, these places were northwest India, Pakistan, the Middle East, western United States, Mexico, and central Asia. 

These results highlighted substantial risks for the affected regional agricultural economies. However, the model also showed that modest changes in irrigation and location of crop growth could meet global food demands despite severe water constraints. Whilst this study simulated a world with frictionless trade, these ideas are important as world leaders must take water constraints into consideration, given how affected everyone will be if we deplete these natural resources. 

Full article: A pathway of global food supply adaptation in a world with increasingly constrained groundwater, Sean WD Turner, Mohamad Hejazi, Katherine Calvin, Page Kyle, Sonny Kim, Science of the Total Environment

Predicting the effect of climate change on THM formation

Climate change will change every aspect of our lives, including our water supply. Predicting what effects may occur is imperative, and quantitative data is necessary to understand the extent and how big adaptations will need to be.

STREAM researcher Maria Valdivia-Garcia investigated one such effect – that of carcinogenic trihalomethanes (THMs). THMs form when chlorine and other disinfectants used in water interact with naturally occurring organic and inorganic matter in water. THMs can cause many health issues, including cancer and reproductive issues, so higher levels would mean a higher health risk. 

Monitoring data was collected from five full-scale Scottish drinking water treatment plants. The data showed a significant correlation between THMs and water temperature, and a separate significant correlation between THMs and dissolved organic carbon concentration. These two correlations were clearly seasonal, which demonstrates that climate can influence THMs formation. 

Laboratory tests were done to quantify the sensitivity of THMs formation to water temperature and dissolved organic carbon concentration. The results of these experiments reproduced the real-world data from the treatment plants, which implies that the quantitative data from the laboratory tests was accurate to real-world conditions. These tests were then combined with existing information about future trends in mean summer temperatures and surface water dissolved organic carbon in the British Isles, so we can estimate global warming’s impact on THMs formation. 

An increase in mean summer temperature will likely increase THMs formation. The mid-range scenario had a 1.8°C temperature increase by 2050, and a 39% THMs formation increase. This escalation would have major implications to potable water around the world. THMs pose a real health risk, which means such an increase would require either accepting the higher risk to human health, or a rise in water treatment costs to maintain the current quality in the potable water supply. If water companies begin to prepare now, lower cost methods could be investigated and put into practice before it becomes a public health concern. 

Full article: Predicted Impact of Climate Change on Trihalomethanes Formation in Drinking Water Treatment, M Valdivia-Garcia, P Weir, DW Graham, D Werner, Scientific Reports

Impact of membrane fouling on separating water from urine

Membranes are used throughout the wastewater treatment industry, and they are suitable for many of the processes. They are often more desirable than the alternative treatments, as they rarely have by-products that require disposal, and do not require any input once in place. However, fouling over time tends to be a large issue and leads to frequent replacement of the membranes. 

What is membrane fouling? This is when the solution being treated is deposited on the surface or in the pores of the membrane, leading to degradation of the membrane’s performance. A degraded membrane is a problem for water treatment, as it will lower the quality of the final product and may prevent it from reaching safety standards. Fouling can be either reversible or irreversible. Reversible fouling can be undone by cleaning the membranes, whereas irreversible fouling means cleaning is not possible and replacement is unavoidable. Membrane fouling is one of the main obstacles when it comes to using this technology, and as a result, research is needed to find ways to slow fouling and clean the membranes.  

Membrane distillation was evaluated for non-sewered sanitation by STREAM researcher Farhad Kamranvand. Waste heat was used to enable the separation of clean water from urine, instead of pressure. 

Whilst membrane fouling did happen when urine was treated, wetting was not evident, and the water quality of the product met the proposed discharge standard despite the high concentration of urine in the experiment. The fouling was also reversible with physical cleaning, which agrees with past studies operating without pressure as the main force. There was a high chemical oxygen demand reduction following faecal contamination, but the mass transfer was impeded and wetting did occur when the quality was compromised. When the urine was contaminated with faecal matter, the mass transfer was delayed, and wetting did occur if the quality was compromised. This suggests faecal contamination should be reduced as much as possible before using this method to separate water and urine. 

Full article: Impact of fouling, cleaning and faecal contamination on the separation of water from urine using thermally driven membrane separation, Farhad Kamranvand et al, Separation Science and Technology

The cost of bacteria-caused drinking water failures

Disease-causing bacteria must be avoided in drinking water supplies, and as a result, investigating bacteria-based failures is essential. The water industry is expected to provide quality assurance and improvement on its current methods wherever possible. However, failures still happen and are found during routine water quality monitoring. These failures have a financial implication for the water companies, however there has been little investigation into what the cost of these failures are and how this impacts the company. 

STREAM researcher Kate Ellis sought to fill this knowledge gap with her research on the cost of bacterial failures. The study focused on failures due to coliform and e. coli being found during routine checks, across five different British water companies. In total, there were 737 failures of this type during the study period. The cost was calculated from the staff hours needed to deal with the failures, the collections of additional samples, transportation, and any additional activities necessary for the place where the sample was being collected. The cost of different types of failures were calculated as well; specifically customer tap failures, service reservoir failures, and water treatment works finished water failures. 

The average costs of the investigations were between £575 (for a customer tap failure) and £4,775 (for a water treatment works finished water failure). These numbers can provide these and other water companies the ability to budget in operational costs for dealing with these failures. Furthermore, the costs can be used to justify the need for increased funding for preventative strategies. Companies may have been reluctant to spend the money on research and implementation of new strategies before, however now the cost can be compared to the cost of the investigation of the failures as well as repairing the issue, and the total cost over time. The comparison of the cost of the two options is likely to make the funding for prevention appear more reasonable, allowing for fewer bacteria related failures in the future. 

Full article: Understanding the costs of investigating coliform and E. coli detections during routine drinking water quality monitoring, Kate Ellis et al., Urban Water Journal