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