Coupling Advanced Oxidation processes with Biological Treatment (WP2)
This WP deals with non-biodegradable and/or toxic wastewater. For such streams alternatives to the conventional activated sludge treatment must be employed. Among the chemical treatments, Advanced Oxidation Processes (AOP) are well known for their capacity for oxidising and mineralising almost any organic contaminant (Gogate and Pandit, 2004 a-b; Legrini et al, 1993; Safardazeh-Amiri et al., 1996). Nevertheless, technical AOP commercial applications are still scarce mainly because of their high costs. Accordingly, several promising cost-cutting approaches have been proposed such as integration of AOP as part of treatment trains that include biological processes. Typically there are two basic approaches. First, a process design, in which the AOP would typically be a pre-treatment of non-biodegradable or toxic wastewater. Once biodegradability has been achieved, the effluent can be transferred to a cheaper biological treatment. The key is to minimise residence time and reagent consumption in the more expensive AOP stage by applying an optimised coupling strategy (Sarria et al., 2003; Esplugas and Ollis, 1997). Second, the AOP can be applied as polishing step after biological treatment for persistent recalcitrant substances. According to a third approach, the AOP step (O3, H2O2/UV) could be placed on the recirculating stream of a biological stage obtaining an integrated-system and not a mere combination of both processes. Other proposed cost-cutting measures are the use of renewable energy sources, i.e. sunlight as irradiation source for TiO2 photo-catalysis and photo-Fenton (Malato et al., 2002), further advances and development of applied reactors and improved plant operation and control strategies to raise the degree of automation and lower the operational costs (Gernjak et al., 2005). In this area, a major need is a scientific rationale on which an "a priori"? choice of the most appropriate treatment should be based.In this WP, wastewater treatment problems common to several industrial sectors will be considered aimed at developing technical solutions based on combination and/or integration of AOPs and biological treatments. The investigated wastewaters as well as the proposed solutions will serve as case studies for more wide-spread applications and will be the following:
1) Photo-Fenton and subsequent biological step with immobilised biomass for treating wastewater heavily contaminated with pesticide, formulation additives and pharmaceutical residues.Solar photo-Fenton method promises to be especially effective due to the aromatic/ phenolic nature of the recalcitrant pollutants. The solar approach is particularly advisable in sunny areas such as southern European Countries. Immobilised biomass is superior to suspended biomass, because sludge age (less sensitivity to conditions changes or temporarily toxic influents) and treatment capacity per volume are substantially higher. In this case the objectives are: -Treat end-users wastewaters as function of their necessities and assess the advantages of the combined treatment approach as compared to a single AOP step. -Improved understanding of how the AOP treatment affects the development of acute toxicity and biodegradability with respect to pollutants’ structures as well for model compounds as for complex wastewater matrix. -New and cheaper approaches for on-line assessment and control of the process increasing the degree of automation. -New insights on the possible formation of halogenated by-products in the AOP step under saline conditions and the bacterial contamination after the biological reactor concerning posterior re-use in agriculture (only pesticide wastewater) and industrial processes (safe application, no biofouling). -Enhanced knowledge about the application of photo-Fenton/biological treatment to saline wastewater. This is very important because many industrial wastewaters have varying degrees of salinity. The performance of photo-Fenton (Maciel et al., 2004) as well as activated sludge systems is different under such conditions and to assess the viability of such an approach is vital to increase respective knowledge.
2) Landfill leachate treatment by the Chito-Biomem-AOP concept.Although landfill leachate cannot be strictly defined as an industrial wastewater, it is one of the most recalcitrant wastes for biotreatment and therefore represents an interesting case study. Furthermore, old leachates having BOD/COD ratios below 0.05 represent an increasing problem across the whole EU community, with leachate generally aging and becoming less treatable. Hence, although it can generally be nitrified (notwithstanding the high and variable ammonia levels) and bacterial population in biofilm reactors can be adapted to this wastewater, it does not lend itself to biotreatment for COD removal above 80%. The selected treatment approach will be a combined process recently developed (Chito-Biomem-AOP concept): in a first step particles are removed by dissolved air flotation, using a biopolymer such as chitosan as coagulant. Chitosan is biodegradable and enhances thereby the biodegradability of the generated sludge. The biopolymer can be used as the primary coagulant or as a coagulant aid. Negatively charged biopolymers such as alginate may be added as flocculants. Improved settling characteristics using biopolymers have been demonstrated in various wastewaters such as raw sewage, dairy wastewater, and storm water. The biopolymers have been shown to be excellent turbidity removers, but less efficient in removing dissolved organic matter compared to the metal-based coagulants. Chitosan and alginate are also known metal chelators with high specificity for heavy metals of environmental concern (e.g. Pb, Hg, Cd, Cr) (Bailey et al. 1999). Subsequently, the dissolved biodegradable compounds in the particle free wastewater/process water are removed in a biofilm airlift suspension reactor. Biomass can be detained by gel entrapment resulting in high biomass concentration (Vogelsang et al., 2000). Detached excess biomass is separated by a microfiltration step and recycled to the particles removal step to be separated there, while non-biodegradable substances enter an AOP polishing step (O3, UV/H2O2) (Tryland et al., in preparation). All treatment steps are compact and the overall efficiency of the system is expected to be very high. The biofilm process is usually significantly less sensitive to rapid changes in substrate concentrations than the activated sludge process (Vogelsang et al., 2000). In this case the specific objectives are: -Treat landfill leachate with the final effluent complying with the legal discharge limits. -Optimise the Chito-Biomem-AOP concept for landfill leachate in lab-scale with focus on treatment efficiency, sludge characteristics and residuals management. -Continuous treatment of landfill leachate in pilot-scale at two landfill sites with the Chito-Biomem-AOP concept. -New insights will be gained concerning long-term stability of the treatment process investigating natural varying conditions concerning process treatment and performance related to the gel-entrapped biofilm.
3) Chemical and Pharmaceutical wastewater treatment by an integrated AOP+ MBR system.Wastewater of the chemical and pharmaceutical industry normally contains solvents, starting chemicals, intermediates and synthesis products. Previous work on the treatment of wastewaters from pharmaceutical industry or wastewater containing drug residues mainly investigated the effects of conventional biological treatments on the abatement of selected compounds (El-Gohary et al., 1995; LaPara et al., 2002; Carballa et al., 2004; Joss et al., 2005). The adequateness of chemical oxidation for the degradation of pharmaceutical compounds in wastewater was also investigated and O3-based treatments were often suggested (Höfl et al., 1997; Akmehmet et al., 2003; Ternes et al., 2003; Andreozzi et al., 2005). Integration of biological and chemical treatment was often indicated as having a high potential in completely degrading the recalcitrant compounds present in these wastewaters. However, most of the experimental work was performed with combination of biological-chemical treatment schemes, rather than with real integrated innovative processes (Gulyas et al., 1995; Rosén et al., 1998; Arslan Alaton et al., 2004; Samuel Suman Ray and Anjaneyulu, 2005).In this WP, the approach will be an integrated one, where an AOP step (O3, UV/H2O2) will be inserted into the recycling stream of a membrane bioreactor (MBR). The advantages of such a system, in addition to cost savings, are linked to its presumable high flexibility, great compactness and expected effectiveness for the treatment of industrial wastewater characterized by high COD loads and significant content of inhibitory and/or recalcitrant pollutants. In this case, the specific objectives are: -Definition and experimental optimization of an integrated process including selected AOPs (O3 and/or UV/H2O2) and enhanced biological degradation (membrane bioreactor, MBR) for the complete treatment of pharmaceutical industrial wastewater (Austep, end-user). -Characterisation of the degradation by-products of model pollutants relevant to the end-user’s wastewater. -Study of the interactions between the proposed AOPs and the biological processes (dosage of chemicals, degradation by-products of the recalcitrant compounds, operational optimization of an integrated AOP/MBR process). -Assessment of the relationships between the performance of the integrated AOP/MBR process and the physical, chemical and microbiological characteristics of the MBR biomass.
Literature
A list of the literature referenced in this text can be found here
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