Hydrogen sulfide is produced by sulfate reducing bacteria, which are mainly associated with the biofilms covering the surfaces in rising mains. Sulfide control strategies commonly used such as chemical dosage are costly for long-term management. The effect of physical and hydraulic conditions of sewers on sulfide formation has been investigated in recent years. One of the key parameters in modelling the formation of hydrogen sulfide is the pipe area- volume ratio (A/V), as this indicates the relative contribution between biofilm and wastewater processes. The A/V is naturally related to the pipe diameter. A high A/V is associated with small pipe diameter, and would lead to a high contribution from the biofilms and hence the potential for high hydrogen sulfide formation. However, it would also decrease the residence time of the wastewater, which would tend to decrease the amount of hydrogen sulfide formed. Based on the results of in-sewer process modelling, this study quantifies the importance of the pipe diameter and pumping strategy for optimal design for rising mains, to minimise hydrogen sulfide production, either to improve the life time for the downstream sewer structures or to minimise the potential chemical dosing needed in the rising mains. The model results from this study show optimal diameter options for both existing rising mains in terms of minimum hydrogen sulfide formation. The sensitivity analysis on model parameter based on the case studies also indicates the most uncertain parameters and COD fractions. Methane is a problem acknowledged in some sewer networks around the world and is particularly of concern in China where sewer explosions can occur. Septic tanks are integrated parts of many Chinese sewer systems and methane is believed to be produced not only in sewer pipes, but also in septic tanks. Work has been done to look at how the anaerobic digestion model can be applied in combinations with sewer processes models to describe such a system. Model simulation results on methane formation in rising mains is similar to reported literature. The field measurements in the Chinese sewer system demonstrated high gas phase hydrogen sulfide and methane concentrations both in gravity systems and rising mains due to the surcharging sewer conditions. Future work has been proposed according to the local problems by discussing the benefits of applying sewer process and anaerobic digestion models based on this study.

Phosphorus (P) is an essential non-substitutable nutrient for all living organisms, but it is also a dwindling non-renewable resource. Approximately two-thirds of the world’s supply of phosphate rock is located in China, Morocco, and the USA. Phosphate rock is included in the EU list of ‘critical raw materials’ and is ranked 20th in an index of commodity price volatility. P recovery from waste water can help alleviate reliance on imported phosphate and reduce vulnerability to fluctuating prices. This project explored the options for P recovery from wastes produced across Thames Water’s waste water treatment plants (WWTPs), the main foci being sludge dewatering liquors and incineration/pyrolysis residues. The research focussed specifically on the Slough WWTP and the operation of a newly installed Ostara system for recovery of P as struvite from dewatering liquors. The Ostara process is designed to operate with centrate PO4-P concentrations above 100 mg/l; to obtain these concentrations chemical coagulant dosing in the enhanced biological nutrient removal process must be reduced. Centrate monitoring following this change showed that Fe concentrations must measure consistently below 1.5 mg/l for PO4-P concentrations to remain steadily above 100mg/l. Following these changes onsite, operational savings and revenue can be produced onsite. Significant operational and maintenance savings totalling to £113K can be made in the first year of operation of the P recovery system in Slough WWTP. Sale of P rich struvite fertiliser produces annual revenue of £20K. Moving beyond the local benefits of P recovery, national benefits of P recovery were quantified. In a national context, a total of 28±1 kt P/year can be recovered from all WWTP waste streams, reducing P fertiliser imports by 36±1%. P recovery from WWTP influent and incinerated sewage sludge ash would reduce P losses to water bodies by 22±2%. Sewage sludge may be incinerated, producing incinerated sewage sludge ash (ISSA), or alternatively pyrolysed to produce sewage sludge char (PSSC). The possibility of recovering P from these residual solids was also investigated. PSSC samples contained significantly more nitrogen and lower heavy metal concentrations than ISSA samples due to the process conditions. The % P extractions from both ISSA and PSSC plateaus at 0.6M and 0.8M H2SO4 acid concentrations, respectively, due to the formation of gypsum on the particles, so that further increase in acid concentrations does not increase P recovery. The knowledge gained through this research has been used to improve the understanding and efficiency of the P recovery system at Slough WWTP. The information learned about pyrolysis residues will be used by Thames Water to develop a novel P recovery process from PSSC. Combined, these findings can impact the industry by creating incentives and inform policies regarding P recovery.

Pharmaceuticals intended for human use are frequently detected in the aquatic environment. This is predominantly from their excretion following ingestion and subsequent discharge in domestic sewage. Wastewater treatment provides an opportunity to control their release to surface waters however, their removal is often incomplete. This thesis addresses this pharmaceutical pathway and the potential impact on the aquatic environment. The progress of bezafibrate, carbamazepine, ciprofloxacin and clarithromycin were monitored through the treatment stages (screened sewage, settled sewage and final effluent) of a large urban wastewater treatment plant (WWTP) and in surface waters up-stream and down-stream of the effluent discharge point. All except clarithromycin were detected in the screened sewage (369 – 2696 ng/L). Reductions in the pharmaceutical concentrations throughout the WWTP (22.5 – 94.3 %) indicate the removal of these compounds is variable. Bezafibrate and carbamazepine were observed at higher concentrations (67.5 - 305.5 ng/L) in surface water down-stream of the effluent discharge point compared to up-stream (31.0 – 116.7 ng/L). The presence of antibiotics in the environment may contribute to the dissemination of antibiotic resistance. The second part of this thesis monitors the prevalence of resistant faecal bacteria through WWTPs and in surface waters. Determination of antibiotic minimum inhibitory concentration (MIC) values for E.coli and E.faecium indicated that the WWTP did not influence the proportions of the resistant bacterial species. Elevated levels of E.coli with acquired ciprofloxacin resistance increased from not detectable in surface waters up-stream to 9.3% down-stream of the WWTP discharge point. The need for standardisation of the interpretation of MIC data is addressed. The potential of ciprofloxacin within surface water to select for ciprofloxacin resistant E.coli were investigated through microcosm studies in the third part of this study. A significant increase (p < 0.05) in the level of resistant E.coli was observed in microcosms exposed to ≥ 5 μg/L ciprofloxacin. At the ciprofloxacin levels typically detected in surface waters receiving treated effluent (<300 ng/L), the levels of resistance amongst E.coli were maintained.

Waste activated sludge (WAS) is an important residue generated from Wastewater Treatment Plants (WWTPs) with a high amount of organic and inorganic resources. In view of this, WAS management systems have changed towards improving the use of waste biomass as a feedstock for bioenergy generation and nutrient recovery and reuse. This study assessed the potential of using WAS as the main feedstock for the generation of high-value chemicals like volatile fatty acids (VFAs), via the carboxylate platform. In order to achieve that, a series of experiments were conducted with the aim to identify the main process variables controlling VFA production in batch and semi-continuous stirred tank reactors (CSTRs). In the first stage, acidogenic fermentations were run for 21 days using iodoform as an inhibitor of methanogenic bacteria, reaching VFAs yields of 0.238 g TVFAs/g TVSWAS with iodoform (CHI3) in a ratio of 6 mg CHI3/g VSS and an Organic Loading Rate (OLR) of 5 g TVSWAS/L. The second stage comprised the acidogenic fermentation of high pressure thermal hydrolysis (HPTH)-WAS under different pH conditions (4-1) with results of 0.415 g VFAs/g TVS at pH 9.0 and C/N=8.77, which emphasize the strong effect that pH has on VFA production and speciation and, on the inhibition of methane (CH4) generation. In order to improve VFAs production from HPTH-WAS, acidogenic co-fermentations at pH 9.0 were conducted using thermally pre-treated food waste and algal biomass (Chlorella vulgaris). Optimum results reported a yield of 0.496 g VFAs/g TVS at C/N=12.72 for fermentations using a blend of 25% HPTH-WAS/75% HPTH-Food waste and 25% HPTH-WAS/75% HPTH-Chlorella vulgaris with VFA yields of 0.378 g VFAs/g TVS, C/N=5.08. This suggests that HPTH pre-treatment and co-fermentation had a positive effect on the final production of VFAs despite of the C/N ratio used. Finally, experiments using semi-CSTR reactors fed with HPTH-WAS at pH 9.0 reported yields of 0.539, 0.328 and 0.364 g VFAs/g TVS for fermentors with OLRs of 0.3, 0.6 and 1.0 g TVS WAS/L·d, respectively. This suggests that increments in OLR have a null effect on VFAs production. Fermentations working with 0.3 g TVS WAS/L·d presented overall VFAs production which stoichiometrically exceeds in 31% the methane produced in AD experiments ran in this project. The OLR presented a null effect on the speciation of the VFAs as acetic acid was present in concentrations above 80% of the carboxylic acids content in all CSTR experiments. These results confirm the potential opportunities for high-value chemicals production from HPTH-WAS as part of the development of the biorefinery concept in existing WWTPs.

Monitoring and improving the microbiological quality and safety of surface waters used for various purposes, including drinking water abstraction and recreation is paramount as degradation may pose a serious risk to human health and cause significant economic losses as a result of the closure of beaches and shellfish harvesting areas. With the aim of providing new knowledge and tools with which to manage more effectively faecal contamination of water resources, this study focused on three goals: 1) determining the fate and suitability of new bioindicators for virus removal during wastewater treatment; 2) elucidating the levels and sources of faecal pollution in the River Tagus (Rio Tejo) using a blend of newly-developed and existing microbial source tracking (MST) markers; and 3) critically evaluating various pretreatments to distinguish between infectious and non-infectious viruses. To this end, raw and treated wastewater were collected and tested for the presence of traditional faecal indicator bacteria (FIB), and four viral bio-indicators (namely, somatic coliphages (SC), GB124 phages, human adenovirus (HAdV) and JC Polyomavirus (JCPyV)). In order to demonstrate whether the novel bio-indicators might be suitable indicators of risk to human health, Norovirus genogroup II (NoVGII) were also analysed, in parallel. FIB, SC and GB124 phages were analysed using standardised culture methods (membrane filtration and plaque assays) and HAdV, JCPyV and NoVGII were analysed using widely used molecular (qPCR) methods. Samples of river water were collected over a thirteen-month period and analysed for both non source-specific indicators of faecal contamination (Escherichia coli (EC), intestinal enterococci (IE), and SC) and source-specific contamination markers ((GB124 phages, HAdV) and four mitochondrial DNA markers (HMMit, CWMit, PigMit and PLMit)). EC, IE, SC and GB124 phages were detected by culture methods and HAdV and mitochondrial markers were detected by molecular (qPCR) methods. Furthermore, domestic animal markers (based on the detection of mitochondrial DNA) were also developed for dog and cat and tested during the catchment study. Finally, in order to determine accurately the level of risk to human health, heat-, chlorine-, and UV-inactivated Enterovirus and Mengovirus were subjected to PCR pre-treatments using enzymatic digestion and viability dyes, in order to determine infectivity. Detection of inactivated Mengovirus (MC0) was performed by RT-qPCR and detection of inactivated Enterovirus (EntV) was performed by both RT-qPCR and cell culture. The results demonstrated that the traditional bacterial indicators (FIB) were more effectively removed during wastewater treatment than GB124 phages, SC, HAdV and JCPyV, the removal levels of which were more similar to those of NoVGII. Spearman’s correlation showed that SC and GB124 phages correlated positively with NoVGII at a relatively high level and that HAdV and EC correlated positively at a moderate level. Discriminant analysis revealed that whilst no organism could predict the presence or absence of NoVGII in treated wastewater, GB124 phages in combination with other parameters did result in higher percentages of correct classification. GB124 phages plus HAdV appeared to be good candidates as alternative indicators of enteric virus removal during wastewater treatment. Results from the catchment study demonstrated that certain sites on the River Tagus are relatively highly impacted by faecal contamination (as indicated by EC, IE and SC concentrations). Moreover, the MST markers revealed that this contamination appears to be not only of human origin, but also originates from a range of other animal sources. The HMMit marker was the most prevalent and was found at the highest mean concentrations, followed by the CWMit marker. Two-way ANOVA revealed a correlation between concentrations of non source-specific indicators (and the CWMit marker) and season. Physico-chemical parameters, such as temperature and UV radiation, were found to be related to to levels of the CWMit, EC, IE, and SC. Interestingly, rainfall levels were found to be related to concentrations within the river of the PLMit marker and of the newly-developed dog and cat markers. Weak to no correlations were found between non source-specific indicators and the various MST markers, providing further evidence that these faecal indicators were unsuitable for determining the source(s) of contamination in this study. In contrast, the relatively high sensitivity and specificity of the mitochondrial DNA markers supported their use as appropriate markers of the origin of faecal contamination in this scenario. The results from the viral infectivity study demonstrated that results of ‘viability PCR’ (involving viability dyes) of chlorine- and UV-treated viruses did not correlate with those from cell culture assay. However, data from RNase-RT-qPCR from chlorine- and UV-inactivated viruses were consistent with the cell culture assay, achieving full PCR signal reduction in several instances. Heat treatment appeared to play an important role, since a significant reduction in the RT-qPCR signal was achieved. Different pre-treatments were able to achieve full removal of RT-qPCR signal for non-infectious heat-treated EntV and MC0. Therefore, enzymatic treatment may represent a rapid and inexpensive tool for discriminating between infectious and non-infectious viruses and as such should improve understanding of risks to human health. This research has demonstrated that the currently-used methodologies and approaches to assess the potential human health impact of wastewater discharges to environmental waters are limited in their ability to predict the prevalence of important agents of human waterborne disease. Furthermore, these findings provide evidence to support the development and application of alternative and potentially more effective approaches, which could better protect human health in the future.

Anaerobic biological processes have been recognized as the most suitable pathway towards sustainable wastewater treatment due to the lower energy required and the lower amounts of biosolids generated when compared to conventional aerobic technologies. The difficulties experienced with the implementation of anaerobic reactors for the treatment of low strength wastewater at low temperatures are related to the deterioration of treatment capacity and effluent quality due to inefficient removal of colloidal matter and biomass washout. Membrane technology can overcome the limitation of anaerobic bioreactors since they retain not only solids but also colloidal and high molecular weight organics. This thesis explores the potential of anaerobic membrane bioreactors as core technology for mainstream wastewater treatment. The impacts of seed sludge, temperatures and bioreactors configuration on treatment efficiency and membrane performance as well as nutrient removal using ion exchange resins are investigated. Cont/d.

During this project, the treatment of a simulated wastewater from soluble starch by a two-phase anaerobic system using an UASB reactor was examined under mesophilic conditions. Prior to seeding the reactors, the pregranulated sludge which was to be used as the inoculum for the acidogenic reactor, was acidified to pH 4.3, using a mixture of volatile fatty acids, to improve the spatial bacteria separation in the system. The two-phase system was studied, first under different organic loads and secondly, in terms of its resistance to the addition of heavy metals. For the first experimetal studies, different organic load were applied to the system, and changes to the microbial ecology of the acidogenic and the methanogenic phase was assessed. The biomass in the methanogenic reactor was mainly composed of fluorescent methanogenic bacteria. In the acidogenic reactor after the start-up period elapsed, no fluorescent bacteria were observed. Two different runs were performed and for each individual run, different OLR were used. For the first run, the organic loads applied to the system were from 3.83 to 30.63 kg COD/m3d, this gave organic loads for the methanogenic reactor of between 4.56 to 44.3 kg COD/m3d. In the second run, the OLR used were from 10 to 16.6 kg COD/m3d for the overall system, and from 13 to 23.35 kg COD/m3d for the methanogenic reactor. Organic loads greater than 15 kg COD/m3d, caused biomass wash-out from both the acidogenic and methanogenic reactor. The best COD removal efficiencies and gas production rates were achieved by the system under OLR of 13.31 kg COD/m3d, with pCOD removal efficiency of 95 % and methane production of 80.2 %. The biogas production was 0.33 m3CH4/kg COD removed. Under high applied organic load, the microbial population of the methanogenic reactor changed, and filamentous foaming bacteria were isolated both from the sludge and the foam that was produced. The species found to be responsible for the foam formation in the anaerobic methanogenic reactor was Microthrix parvicella, which was identified using the Neisser test and Scanning Electron Microscopy (SEM). For the second part of this experimental work, copper and lead were used as toxic elements. These two heavy metals were choose due to the fact that they are subproducts of many industries and can cause significant environmental problems. Copper and lead were used as the acetates and chlorides to study the effect of these heavy metals when they were combined with different anions. It was found that the combination of copper and lead as chlorides were more toxic to the anaerobic treatment than when they were present as acetate. Also, it was found that the two heavy metals used were toxic to the acidogenic phase and not to the methanogenic phase.

No description available.

Poly(vinylidene fluoride) (PVDF) membranes have been intensively investigated and commercialised with broad applications in water purification and wastewater treatment for decades due to its outstanding properties. Currently, PVDF membranes are mainly produced by the phase inversion technique, which is predominant in both laboratory research and industrial manufacturing. Various modification methods based on the phase inversion technique have also been developed to improve the membrane performances, but these improvements are incremental and there have been no important breakthroughs during the past decade. This thesis first explores the preparation of reinforced PVDF flat sheet membranes by blending nanoclay followed by the phase inversion process. Although the membranes showed improved water permeation flux and enhanced abrasion resistance, further improvements are limited by the phase inversion technique itself. Consequently, a new concept of membrane manufacturing procedure has been proposed by combining unidirectional crystallisation of green solvent and polymer diffusion. The new method uses crystallites of a solvent dimethyl sulfoxide with controlled sizes as pore templates to create enormous nanosized flow passages. It follows a completely different pore formation mechanism and therefore overcomes the drawbacks of the phase inversion technique. The resultant PVDF membranes have an asymmetric structure composed of a highly porous separation layer and gradually opened micro-channels. Due to the unique structure, the prepared membranes showed excellent permeation performances and mechanical properties overwhelming commercial PVDF membranes prepared by the phase inversion technique. The filtration performance of the PVDF membranes can be further improved by modification of the membrane material, for example, by blending polyethylene glycol in the dope solution. The obtained membrane with pore size of 36 nm showed extraordinary high flux of 1711 L/m2h and could withstand 35 bar in the test. Moreover, the new manufacturing process is of much fewer influencing factors compared to the phase inversion approach and thus highly reliable and repeatable. In principle, it is also applicable to other common polymeric membrane materials such as polyethersulfone and cellulose acetate.

This thesis considers the problem of modelling bioreactors with complex mixing and biokinetic growth based on both soluble nutrients and photosynthesis. From the results of investigations performed on the different modelling methods for nutrient and photosynthesis dependent biomass growth a method of coupling the two biokinetic models was proposed. This new photosynthesis-nutrient (PN) model was then investigated, validated and determined capable of predicting growth characteristics dependent on both nutrient and photosynthetic processes. Additionally an investigation into the factors which may influence the results when using computational fluid dynamics (CFD) to model the flow field within a gas-lift bioreactor was performed. It was determined that one of the main factors which must be considered when modelling bioreactors with boundary layer flow separation is the choice of turbulence model. In the case presented here it was found that the transition SST turbulence model provided the best results with the k-w SST also performing well. Finally, a method of coupling the PN and CFD models was proposed and investigated. The photosynthesis-nutrient-hydrodynamic (PNH) model also incorporated a model for diffusion of light within the bioreactor to allow for investigations into the effects of light absorption and scattering within the bioreactor and how mixing affects the active biomass. Further investigation of this new PNH model determined that the coupling of the biokinetics and flow field provided some insight into the ability of a well-mixed bioreactor to counter low light penetration to an extent.