• Energy Research

Rapid population growth invokes the need for a vast amount of water conservation. Many centralized water treatment systems will reach their limits and face difficulties to provide clean industrial water to rural areas. The infrastructure for water distribution is dilapidated in many regions and only little of the wastewater is currently being recycled. One solution could be the expansion of decentralized membrane bioreactor (MBR) systems in peri-urban areas. MBR achieves excellent water qualities, whereas the comparatively high energy consumption is the main drawback. Therefore, MBR plants need to be optimized in their specific energy consumption to obtain a high degree of self-sufficiency for decentralized locations. There is a dire need for innovative controlling strategies and efficient coupling with energy supply systems through novel applications. This chapter will highlight the basic approaches to reduce the MBR's overall energy consumption and ways to establish sustainable, autonomous operations without sacrificing the process quality.

Membrane bioreactor (MBR) technology has attracted great attention over the last 3 decades and achieved rapid growth in an increasing number of practical small- and large-scale applications worldwide. However, its application in Sub-Saharan Africa as well as in aquaculture was so far limited. The installation and operation of a pilot membrane bioreactor (MBR) in Kisumu, Kenya, adopts an integrated approach by providing an integral, sustainable, cost-effective, and robust solution for water sanitation, which also meets the demand for clean water in the fish processing industry, aquaculture, and irrigation. The innovative system comprises a pilot MBR coupled with a recirculating aquaculture system (RAS) which is linked to a 14.3 kW photovoltaic (PV) system, including a 30 kWh Li battery storage to supply sustainable energy. The RAS is able to recirculate 90-95% of its water volume; only the water loss through evaporation and drum filter back flushing has to be replaced. To compensate for this water deficit, the MBR treats domestic wastewater for further reuse. Additionally, excess MBR treated water was used for irrigating a variety of local vegetables and could be also used in fish processing plants. The pilot-scale MBR plant with around 6 m2 submerged commercial UF polyethersulfone (PES) membranes provides treated water in basic agreement with Food and Agriculture Organization (FAO) standards for irrigation and aquaculture, showing no adverse effects on tilapia fingerlings production. A novel membrane module with a low-fouling coating technology is operating stably but has not yet shown improved performance compared to the commercial one.

To develop easy-to-implement and low-energy water treatment plants, pilot trials for groundwater desalination and arsenic removal were carried out at the Mekong Delta in Vietnam. Desalination was conducted by membrane capacitive deionization (MCDI), which can show low specific energy consumption (SEC) compared to other desalination technologies. Anoxic groundwater with elevated As(III) and dissolved iron (Fe(II)) was treated using a pre-oxidation/adsorption step called subsurface arsenic removal (SAR). The main advantage of the in situ SAR process is that no As-laden waste is produced. The two different qualities of the treated water from two different stages of the pilot plant can be used for various purposes and can be modularly adjusted in volume according to requirements. The pilot plant was operated using a solar PV system and a small wind turbine. Results show that SAR can reduce the As- and the Fe-concentration to below drinking water limits. The MCDI lowers the total dissolved solids (TDSs) concentration of 1560-188 mg/L. The overall process (well pump to product tap) needs an SEC = 3.97 kWh/m3, which is supplied (127%) by renewable energy.