Background

In conventional biological wastewater treatment systems, aerobic and anoxic conditions are usually employed to remove organic matter and nutrients. Such processes are characterized by significant environmental and carbon footprint, owing to the oxygen requirements and to the emissions of CO2, resulting from the biodegradation process. This trend must is beginning to change by focusing research on processes that promote the environmental and economical sustainability. The adoption of biological wastewater treatment processes having low carbon footprint requirements is an interesting alternative that is expected to gain more attention in the near future, particularly as the concern for global warming is increasing and as the efficiency of energy demanding technologies is questioned. In parallel, the co-treatment of waste and wastewater using anaerobic reactors further reduces the environmental burden particularly in small and decentralized communities. In the past, the adoption of the one stage anaerobic system for wastewater treatment has resulted in several cases in treated effluent of low quality, thus limiting its reuse options. This necessitates the adoption of appropriate post-treatment measures. Low environmental footprint processes that provide high level of treated products using suitable post-treatment has received limited research attention. LEF-BIOWASTE shall focus on the development and evaluation of low environmental and carbon footprint biological treatment processes for the co-treatment of municipal wastewater and biodegradable organic waste (BOW). Specifically the following processes shall be examined:

  1. Up-flow anaerobic sludge blanket (UASB): Anaerobic digestion is a well-established process which is suitable for the treatment of high strength wastewater, and wastewater containing high levels of solid matter. The use of anaerobic processes for the treatment of low strength wastewater such as municipal and household wastewater has also been established in tropical and sub-tropical regions, where wastewater temperatures are above 20oC. Different anaerobic digester technologies are available including the UASB, expanded granular sludge blanket (EGSB), two stage anaerobic processes. The technological and economic advantages of the UASB include significant energy savings compared to aerobic treatment systems since aeration is not used, translating into low operational cost, low capital cost, significant energy recovery due to biogas production, low amount of produced sludge and subsequently low sludge handling costs compared to conventional activated sludge processes (CASPs). The UASB process can be employed both in urban areas for the centralized treatment of wastewater and biodegradable organic waste (BOW) and in rural areas for the decentralized treatment of domestic wastewater and BOW. Despite its advantages, the UASB process has also certain critical deficiencies. Specifically, it does not provide a complete solution to the problem of wastewater treatment since the treated effluent requires further post-treatment in order to remove remaining organic matter, nutrients and pathogens and to acquire the desired characteristics for reuse purposes. Other disadvantages include odour problems and the limited experience concerning full scale systems application at moderate to low temperatures.
  2. Sequential batch reactor (SBR) for the post treatment of the anaerobic effluents. The SBR process is also a well-established wastewater treatment process. Its use only as a post treatment stage of the resulting effluent of the UASB or of other anaerobic effluents (e.g. sludge reject water) (rather than as a one-stage treatment system of wastewater) has significant cost savings due to much lower aeration requirements and also due to the energy benefits of biogas production during the anaerobic stage. The main role of the SBR system is to ensure that the treated effluent satisfies the reuse guidelines with a very high removal of organic matter, as well as of other constituents that are poorly removed by the anaerobic treatment, such as nutrients, reduced inorganic compounds.
  3. Short-cut nitrogen and phosphorus removal: Instead of the conventional nitrification/denitrification process for nitrogen removal, the short-cut nitrogen removal processes shall be employed. A short-cut nitrification is required in order to convert ammonium contained in wastewater to nitrite and thus provide enough nitrite for the subsequent anaerobic ammonium oxidation (Anammox) process or the heterotrophic denitritation. In the Anammox process ammonium is oxidized by nitrite instead of oxygen that is the case in the traditional nitrification process. Anammox is an autotrophic nitrogen removal process performed by the Anammox bacteria, which are characterized by an extremely slow growth rate. The short-cut nitrogen removal processes are characterized by lower aeration (and thus energy) requirements, lower (or no) external carbon source requirements and lower excess sludge production.      

 

 Schematic representation of nitritation/denitritation and of nitritation/anammox

 

LEF-BIOWASTE aims to combine the aforementioned processes of UASB-SBR in an innovative treatment system that will be able to treat both wastewater and BOW with significant energy savings and very low carbon footprint requirements. The UASB-SBR process shall first be developed as a bench scale system in the laboratory under very controlled conditions and then it will be further examined in a pilot scale system. LEF-BIOWASTE shall examine all biological processes of the UASB-SBR system and particularly short-cut nitrogen removal processes.