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