Emerging Technology for Energy Recovery from Sludge

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While the South African sanitation sector has made some progress in water and energy recovery from sanitation waste (particularly from wastewater from sewered systems), recovery of nutrients and other high value products still lags behind for both sewered and non-sewered sanitation waste. Efforts to implement comprehensive resource recovery are sporadic and currently limited to the large Metros. There is no understanding of the quality and quantity of available sanitation waste and the potential resources that can be recovered, appropriate technologies and the impact of the market and current legal and regulatory framework. To ensure that resource recovery is successfully adopted at a national level and contributes to adoption of circular economy (CE) principles, sanitation sensitive design and sustainable cities, it is necessary to develop coherent strategies and a National Policy to assist municipalities. TruSense was awarded this project to address these national gaps and develop a national policy and framework that assists municipalities recover not only energy and nutrients but high value materials such as bioplastics, biopolymers, heavy metals, protein and chemicals from sanitation waste. The project involved (a) Review of local and international sanitation waste recovery regulations, identification of local gaps and proposed solutions (b) Assessment of the quantity and quality of sanitation waste (both sewered and non-sewered) (b) Identification of feasible options and technologies and the quantity and quality of resources recovered (c ) Market mapping and value chain analysis and (d) Development of strategies with recommendations on regulatory, policy, organizational changes, investments, incentives and infrastructure needs for resource recovery.

Approximately 31% of South African households use pit latrines, totalling about 4 million nationally. Many pit latrines in poor urban areas are full and need immediate emptying, with faecal sludge (FS) transported to centralized facilities for treatment. FS management is a significant challenge for South African municipalities. Since 2010, research has focused on developing innovative, sustainable FS treatment technologies that encourage the use of treatment by-products. Technologies like black soldier fly larvae, thermal drying, and solar drying have been trialled but their full-scale sustainability is still under investigation.

As part of the ongoing effort to find effective FS treatment technologies, the client funded this project to evaluate the enhanced hydrothermal polymerization (EHTP) process for treating FS from pit latrines. A pilot reactor was installed at a WWTP processing FS from VIP latrines in 2 municipalities, as well as FS mixed with primary sludge (PS) and waste activated sludge (WAS). Analyses showed that the EHTP process effectively sterilized the FS, producing hydrochar and effluent that met ISO 3180 and DWS guidelines. The hydrochar had a higher calorific value and nutrient content than the FS, making it suitable for use as a biofuel, soil conditioner, or building material. Co-processing FS with wastewater sludge improved the hydrochar’s characteristics.

The project demonstrated that the EHTP process can effectively treat FS, creating opportunities for adopting circular economy principles in sanitation and waste management in low-income communities 

 Conventional technologies used in sludge treatment are not consistently efficient in removing all EDCs of concern. Residual EDCs can therefore enter the environment through sludge disposal routes such as land application where the EDCs can potential accumulate and leach into ground water or get taken up by plants. This concern has consequently stimulated research into the efficiency of EDCs from wastewater sludge in recent years.Themajority of the research has however focused on removal of EDCs by conventional treatment processes like anaerobic digestion with very little research on alternative treatment technologies. In South Africa, minimal research has been carried out on EDCs in wastewater and sludge as well as associated technologies that can enhance EDC removal at conventional WWTPs. Considering that the sludge management regulations in South Africa advocate for beneficial utilization including land disposal and reuse for agriculture, understanding the levels of EDCs in treated sludge and measures to lower them is important. To address some of the research gaps, this project was funded as part of the ongoing research on EDCs. The main objectives of the project were to: 

•Evaluate the efficiency of an emerging sludge treatment technology at pilot scale in removing targeted EDCs from various types of sludge generated at a local WWTP  

•Compare the results from the pilot study with conventional anaerobic digestion as well as other technologies 

The scope of the project included technical and economic evaluation of implementing each technology at a typical South African WWTP, conducting a knowledge dissemination workshop and preparation of a project report. The emerging enhanced hydrothermal polymerisation Polymeric Carbon Solid (PCS) process was selected for evaluation. A previous study by Musvoto et al. (2018) at laboratory scale showed that the PCS technology is capable of achieving67 – 100% removal of some EDCs (carbamazepine, methylparaben, Bisphenol A and chloramphenicol) from various sludge types. A 60 litre pilot reactor was located at a local municipality's WWTP. Batches of primary sludge (PS), waste activated sludge (WAS), mixed PS and WAS and anaerobically digested sludge (DS) from the plant were processed in the pilot reactor. Both the sludge feedstock and produced hydrochar were analysed for selected target EDCs based on previous research at Daspoort WWTP as well as compounds of concern identified by the GWRC.