Search

Abstract: The demand for fresh water is steadily increasing as a result of the increasing human populations and activities. On the other hand, water sources are limited, especially as the global warming continues to change the quantities and distribution of water all over the world. Therefore, focusing the research efforts on finding alternate water sources is crucial. Utilizing used waters that were previously considered wastewater has a great potential to reduce the dependency on fresh water sources. Among these used waters is greywater, which is used water generated from domestic activities such as laundry, washing and bathing (excluding toilet and kitchen waste). Due to exclusion of major sources of contaminants, greywater has lower levels of contaminations given its considerably large volumes (50-80% of domestic combined wastewater). Therefore, greywater as a higher potential than domestic wastewater for on-site treatment and reuse. Thus, effective treatment technologies are needed to mitigate the health and environmental risks associated with reclaimed greywater. In this study, a new design of activated carbon biofilters composed of two zones (unsaturated and saturated) in a single stage was developed for greywater on-site treatment to provide high-quality effluent that is safe for potential domestic uses or safe discharge into the environment. The treatment capacity of the developed technology was tested by evaluating its capability in removing major nutrients under different loading rates where the system achieved an average TCOD removal of 98% and complete nutrients removal throughout its 253 days of operation at highest hydraulic and organic loadings of 1.2 m3 m-2 d-1 and 3.5 kg COD m-2 d-1, respectively. The capacity of the system to reduce pathogens was also tested against five pathogen surrogates representing four groups of pathogens (human skin-associated bacteria, human enteric bacteria, viruses, and protozoan cysts and oocysts). The system showed a range of reduction towards the pathogen surrogates ranging from no reduction in viruses to a log reduction of 3.4 in protozoan cysts and oocysts with an intermediate log reduction of 0.26-1.13 in bacteria. The individual capacity of each of the unsaturated and saturated zones was identified for reducing the major nutrients and pathogen surrogates. Biofilm development and activity was also profiled along the biofilter’s depth to show that a well-functioning biofilm developed within the system, and its mass and activity increased over time with the highest values observed at the top layers. The microbial community structure along the depth of the biofilter was analysed and results were reported at class and genus levels where the key microbes were revealed and the bacterial genus Oleomonas was found to predominate the system due to its unique and advantageous attributes. The treatment processes taking place within the system were identified and their kinetics were measured to help understand the behaviour of the biofilter and potentially facilitate its design and operation. Since sorption and biodegradation are the two main treatment processes in biofilters, their individual contribution to the overall treatment was quantified. In a mechanistic study conducted on BAC media collected from the GAC biofilter, biodegradation was found to contribute 26% and 10% after 1 h and 24 h of treatment, respectively, while the rest was attributed to sorption processes. This finding suggested that intermittent dosing of greywater to the biofilter is preferable due to the difference in removal capacities to allow for bioregeneration of the BAC media by the biodegradation process. A new method was developed to study the adsorption equilibrium and kinetics while completely eliminating the impact of the biofilms surrounding the GAC media. Testing the equilibrium adsorption experimental results against four isotherm models revealed that the Freundlich isotherm was found to best represent the equilibrium adsorption data. A study on the kinetics of isotherm showed that the pseudo-second order and intraparticle diffusion models were found to fit the adsorption kinetics. Intraparticle pore diffusion was found to be the rate limiting step after a few hours of treatment.