Rheological characterisation of synthetic and fresh faeces to inform on solids management strategies for non-sewered sanitation systems.

In order to obviate the economic issues associated with pit latrine emptying and transport such as high water additions and rheologically difficult sludge properties, the implications of prompt solid/liquid separation were investigated. This was achieved through rheological characterisation of fresh human faeces and synthetic faeces, and comparison with aged faecal sludges. Shear yield stress, thixotropy and post-shear structural recovery were characterised for a total solids (TS) concentration range of 5-35% total solids (TS) and stickiness yield stress was determined for concentrations up to 100% TS. Fresh faeces rheology proved to be favourable when compared to aged matrices, evidenced by a lower shear yield stress and higher gel point solids concentration, suggesting that aging could alter the physico-chemical properties of faecal sludge. Fresh and synthetic faeces exhibited similar shear thinning, thixotropic behaviour with the majority of structural breakdown occurring at a low shear rate of 10 s-1, and the extent increasing with higher solids concentrations. At 32% TS, fresh faeces shear yield stress was permanently reduced by 80%, suggesting that low shear pumping could reduce the energy demand required for faeces transport. The sticky phase, which represents the region to avoid faecal transport and mechanical drying processes, was identified to range from 30 to 50% TS, with 25% TS as ideal to commence dewatering processes. This also coincides with the average solids concentration of faeces, which is achievable by source separation. This study has identified that handling of fresh faeces as opposed to aged faecal sludges would result in economic and environmental benefits, with energy, water and labour savings.

The determination of nonylphenol and its precursors in a trickling filter wastewater treatment process.

An ultra performance liquid chromatography method coupled to a triple quadrupole mass spectrometer was developed to determine nonylphenol and 15 of its possible precursors (nonylphenol ethoxylates and nonylphenol carboxylates) in aqueous and particulate wastewater matrices. Final effluent method detection limits for all compounds ranged from 1.4 to 17.4 ng l(-1) in aqueous phases and from 1.4 to 39.4 ng g(-1) in particulate phases of samples. The method was used to measure the performance of a trickling filter wastewater treatment works, which are not routinely monitored despite their extensive usage. Relatively good removals of nonylphenol were observed over the biological secondary treatment process, accounting for a 53 % reduction. However, only an 8 % reduction in total nonylphenolic compound load was observed. This was explained by a shortening in ethoxylate chain length which initiated production of shorter polyethoxylates ranging from 1 to 4 ethoxylate units in length in final effluents. Modelling the possible impact of trickling filter discharge demonstrated that the nonylphenol environmental quality standard may be exceeded in receiving waters with low dilution ratios. In addition, there is a possibility that the EQS can be exceeded several kilometres downstream of the mixing zone due to the biotransformation of readily degradable short-chained precursors. This accentuates the need to monitor 'non-priority' parent compounds in wastewater treatment works since monitoring nonylphenol alone can give a false indication of process performance. It is thus recommended that future process performance monitoring and optimisation is undertaken using the full suite of nonylphenolic moieties which this method can facilitate.

Fate of alkylphenolic compounds during activated sludge treatment: impact of loading and organic composition.

The impact of loading and organic composition on the fate of alkylphenolic compounds in the activated sludge plant (ASP) has been studied. Three ASP designs comprising carbonaceous, carbonaceous/nitrification, and carbonaceous/nitrification/denitrification treatment were examined to demonstrate the impact of increasing levels of process complexity and to incorporate a spectrum of loading conditions. Based on mass balance, overall biodegradation efficiencies for nonylphenol ethoxylates (NPEOs), short chain carboxylates (NP(1-3)EC) and nonylphenol (NP) were 37%, 59%, and 27% for the carbonaceous, carbonaceous/nitrification, and carbonaceous/nitrification/denitrification ASP, respectively. The presence of a rich community of ammonia oxidizing bacteria does not necessarily facilitate effective alkylphenolic compound degradation. However, a clear correlation between alkylphenolic compound loading and long chain ethoxylate compound biodegradation was determined at the three ASPs, indicating that at higher initial alkylphenolic compound concentrations (or load), greater ethoxylate biotransformation can occur. In addition, the impact of settled sewage organic composition on alkylphenolic compound removal was evaluated. A correlation between the ratio of chemical oxygen demand (COD) to alkylphenolic compound concentration and biomass activity was determined, demonstrating the inhibiting effect of bulk organic matter on alkylphenol polyethoxylate transformation activity. At all three ASPs the biodegradation pathway proposed involves the preferential biodegradation of the amphiphilic ethoxylated compounds, after which the preferential attack of the lipophilic akylphenol moiety occurs. The extent of ethoxylate biodegradation is driven by the initial alkylphenolic compound concentration and the proportion of COD constituted by the alkylphenol polyethoxylates (APEOs) and their metabolites relative to the bulk organic concentration of the sewage composed of proteins, acids, fats, and polysaccharides. Secondary effluents from this study are characterized by low bulk organic concentrations and comparatively high micropollutant concentrations. Based on the biodegradation mechanism proposed in this study, application of high rate tertiary biological treatment processes to secondary effluents characterized by low bulk organic concentrations and comparatively high APEO concentrations is predicted to provide a sustainable solution to micropollutant removal.

On the compressional rheology of fresh faeces: Evidence for improving community scale sanitation through localised dewatering.

Non-sewered sanitation is currently dependant upon pit latrine emptying, the safety of which is compromised by the high costs of faecal sludge transport to centralised treatment facilities. Transport in turn is hindered by the complex rheology of pit latrine sludge. This study therefore characterised the compressional rheology of fresh faeces and modelled the implications for passive (gravity) or mechanical (forced) solid/liquid separation. This informs on the viability of decentralising dewatering for more efficient volume reduction and improving the economics of transportation. The gel point (ϕg) is the solids concentration where the material has a networked structure and signifies the point when mechanical intervention is required for further solid-liquid separation. For fresh faeces, ϕg ranged between 6.3 and 15.6% total solids (TS) concentration. This is significantly higher than the ϕg observed for wastewater sludge at centralised facilities, and it implies that passive gravity driven processes can suffice to improve localised dewatering. The kinetics of passive sedimentation of faecal material were modelled and illustrate thickening from 3 to 10% TS concentration in <0.5 h. This highlights that early intervention to thicken faeces while fresh can improve solid/liquid separation efficiency. Filtration of fresh faeces was characterised by lengthy cake filtration times and comparably short compression times, more similar to mineral slurries than to wastewater sludge. Consequently, fresh faeces presented improved dewatering characteristics, supporting higher final cake solids concentrations and improved dewatering kinetics. By complementing thickening with 300 kPa filtration, a 1.4 cm thick 25% TS product could be achieved in <24 h. Investigation of matrix properties highlighted that increased conductivity (e.g. exposure to urine) negatively influenced dewaterability, an effect which could be mitigated by introducing solid-liquid separation earlier. The thermodynamically favourable compressional rheology of fresh faeces has identified that focussing on localised dewatering could radically improve the economics of faecal sludge management, primarily through reducing transport costs.

Improving energy efficiency of electrochemical blackwater disinfection through sequential reduction of suspended solids and chemical oxygen demand.

Onsite reuse of blackwater requires removal of considerable amounts of suspended solids and organic material in addition to inactivation of pathogens. Previously, we showed that electrochemical treatment could be used for effective pathogen inactivation in blackwater, but was inadequate to remove solids and organics to emerging industry standards. Further, we found that as solids and organics accumulate with repeated recycling, electrochemical treatment becomes less energetically sustainable. Here, we describe a pilot study in which concentrated blackwater is pretreated with ultrafiltration and granular activated carbon prior to electrochemical disinfection, and show that this combination of treatments removes 75-99% of chemical oxygen demand, 92-100% of total suspended solids, and improves the energy efficiency of electrochemical blackwater treatment by an order of magnitude.

Quantifying the performance of a hybrid anion exchanger/adsorbent for phosphorus removal using mass spectrometry coupled with batch kinetic trials.

Increasingly stricter phosphorus discharge limits represent a significant challenge for the wastewater industry. Hybrid media comprising anionic exchange resins with dispersions of hydrated ferric oxide nanoparticles have been shown to selectively remove phosphorus from wastewaters, and display greater capacity and operational capability than both conventional treatment techniques and other ferric-based adsorbent materials. Spectrographic analyses of the internal surfaces of a hybrid media during kinetic experiments show that the adsorption of phosphorus is very rapid, utilising 54% of the total capacity of the media within the first 15 min and 95% within the first 60 min. These analyses demonstrate the importance of intraparticle diffusion on the overall rate in relation to the penetration of phosphorus. Operational capacity is a function of the target effluent phosphorus concentration and for 0.1 mg P L-1, this is [Formula: see text], which is 8-13% of the exhaustive capacity. The adsorbed phosphorus can be selectively recovered, offering a potential route to recycle this important nutrient. The main implication of the work is that the ferric nanoparticle adsorbent can provide a highly effective means of achieving a final effluent phosphorus concentration of 0.1 mg P L-1, even when treating sewage effluent at 5 mg P L-1.

Denitrification from drinking water using a membrane bioreactor: chemical and biochemical feasibility.

Interest is growing in developing membrane bioreactors (MBRs) to replace ion exchange for nitrate removal from drinking water. However, few published studies have successfully managed to retain exogenous or biologically derived carbon. This study determined an optimum C:N by substrate breakthrough rather than maximum nitrate removal. By dosing

Influence of substrate on fouling in anoxic immersed membrane bioreactors.

The influence of carbon substrate chemistry on membrane bioreactor (MBR) fouling in anoxic conditions has been evaluated. The use of a weak carboxylic acid (acetic acid) resulted in the production of large open-floc structures (up to 508microm) that were susceptible to breakage. Primary particles (d(10) and d(20) particle sizes, 5.5+/-1.3 and 15.3+/-8.2microm, respectively) and macromolecular soluble microbial products (SMPs) were generated, directly impacting on membrane fouling. The use of a primary alcohol (ethanol), on the other hand, encouraged the growth of flocs similar to activated sludge. These flocs produced low concentrations of primary particles (d(10) and d(20) particle sizes, 120.6+/-36.1 and 185.2+/-62.7microm, respectively) and high-molecular-weight SMP, and the particles had sufficient mechanical integrity to withstand shear. Consequently, the use of ethanol resulted in sufficient suppression of fouling to extend the filtration time by a factor of three. An increase in MLSS concentration did not directly impact upon fouling when operating with ethanol, primarily because of the low concentration of particulate matter produced.

Biogas upgrading by chemical absorption using ammonia rich absorbents derived from wastewater.

The use of ammonia (NH3) rich wastewaters as an ecological chemical absorption solvent for the selective extraction of carbon dioxide (CO2) during biogas upgrading to 'biomethane' has been studied. Aqueous ammonia absorbents of up to 10,000 gNH3 m(-3) demonstrated CO2 absorption rates higher than recorded in the literature for packed columns using 20,000-80,000 g NH3 m(-3) which can be ascribed to the process intensification provided by the hollow fibre membrane contactor used in this study to support absorption. Centrifuge return liquors (2325 g m(-3) ionised ammonium, NH4(+)) and a regenerant (477 gNH4(+) m(-3)) produced from a cationic ion exchanger used to harvest NH4(+) from crude wastewater were also tested. Carbon dioxide fluxes measured for both wastewaters compared reasonably with analogue ammonia absorption solvents of equivalent NH3 concentration. Importantly, this demonstrates that ammonia rich wastewaters can facilitate chemically enhanced CO2 separation which eliminates the need for costly exogenic chemicals or complex chemical handling which are critical barriers to implementation of chemical absorption. When testing NH3 analogues, the potential to recover the reaction product ammonium bicarbonate (NH4HCO3) in crystalline form was also illustrated. This is significant as it suggests a new pathway for ammonia separation which avoids biological nitrification and produces ammonia stabilised into a commercially viable fertiliser (NH4HCO3). However, in real ammonia rich wastewaters, sodium bicarbonate and calcium carbonate were preferentially formed over NH4HCO3 although it is proposed that NH4HCO3 can be preferentially formed by manipulating both ion exchange and absorbent chemistry.

Obtaining process mass balances of pharmaceuticals and triclosan to determine their fate during wastewater treatment.

To better understand pharmaceutical fate during wastewater treatment, analysis in both aqueous and particulate phases is needed. Reported herein is a multi-residue method for the determination of ten pharmaceutical drugs and the personal care product triclosan in wastewater matrices. Method quantitation limits ranged from 7.6 to 76.6 ng l(-1) for aqueous phases and from 7.0 to 96.7 ng g(-1) for particulate phases. The analytical method was applied to attain a complete process mass balance of a pilot-scale activated sludge plant (ASP) operated under controlled conditions. The mass balance (inclusive of aqueous and particulate concentrations at all sample points) was used to diagnose removal, revealing pharmaceuticals to be separable into three fate pathways: (a) biological degradation, (b) sorption onto activated sludge and (c) resistant to removal from the aqueous phase. These differences in fate behaviour explained a broad range of secondary removal observed (-8 to 99%). The ASP was also simultaneously compared to a full-scale trickling filter (TF) works whilst receiving the same influent wastewater. Performance of the ASP and TF was similar, achieving total pharmaceutical removals of 253 and 249 µg g(-1) biochemical oxygen demand (BOD) removed, respectively. This corresponded with reductions in total pharmaceutical load of 91 and 90% (ANOVA, p-value>0.05). Interestingly, despite low suspended solid concentrations final effluents of both the ASP and TF contained significant concentrations of some chemicals in the particulate phase. Individually, triclosan and the antibiotics ofloxacin and ciprofloxacin were within the particulate phase of effluents at concentrations ranging from 26 to 296 ng l(-1).

Assessing potential modifications to the activated sludge process to improve simultaneous removal of a diverse range of micropollutants.

It is proposed that wastewater treatment facilities meet legislated discharge limits for a range of micropollutants. However, the heterogeneity of these micropollutants in wastewaters make removal difficult to predict since their chemistry is so diverse. In this study, a range of organic and inorganic micropollutants known to be preferentially removed via different mechanisms were selected to challenge the activated sludge process (ASP) and determine its potential to achieve simultaneous micropollutant removal. At a fixed hydraulic retention time (HRT) of 8 h, the influence of an increase in solids retention time (SRT) on removal was evaluated. Maximum achievable micropollutant removal was recorded for all chemicals (estrogens, nonylphenolics and metals) at the highest SRT studied (27 days). Also, optimisation of HRT by extension to 24 h further augmented organic biodegradation. Most notable was the enhancement in removal of the considerably recalcitrant synthetic estrogen 17α-ethinylestradiol which increased to 65 ± 19%. Regression analysis indicates that this enhanced micropollutant behaviour is ostensibly related to the concomitant reduction in food: microorganism ratio. Interestingly, extended HRT also initiated nonylphenol biodegradation which has not been consistently observed previously in real wastewaters. However, extending HRT increased the solubilisation of particulate bound metals, increasing effluent aqueous metals concentrations (i.e., 0.45 µm filtered) by >100%. This is significant as only the aqueous metal phase is to be considered for environmental compliance. Consequently, identification of an optimum process condition for generic micropollutant removal is expected to favour a more integrated approach where upstream process unit optimisation (i.e., primary sedimentation) is demanded to reduce loading of the particle bound metal phase onto the ASP, thereby enabling longer HRT in the ASP to be considered for optimum removal of organic micropollutants.

Diagnostic investigation of steroid estrogen removal by activated sludge at varying solids retention time.

The impact of solids retention time (SRT) on estrone (E1), 17ß-estradiol (E2), estriol (E3) and 17α-ethinylestradiol (EE2) removal in an activated sludge plant (ASP) was examined using a pilot plant to closely control operation. Exsitu analytical methods were simultaneously used to enable discrimination of the dominant mechanisms governing estrogen removal following transitions in SRT from short (3d) to medium (10d) and long (27d) SRTs which broadly represent those encountered at full-scale. Total estrogen (∑EST, i.e., sum of E1, E2, E3 and EE2) removals which account for aqueous and particulate concentrations were 70±8, 95±1 and 93±2% at 3, 10 and 27d SRTs respectively. The improved removal observed following an SRT increase from 3 to 10d was attributable to the augmented biodegradation of the natural estrogens E1 and E2. Interestingly, estrogen biodegradation per bacterial cell increased with SRT. These were 499, 1361 and 1750ng 10(12) viable cells(-1)d(-1). This indicated an improved efficiency of the same group or the development of a more responsive group of bacteria. In this study no improvement in absolute ∑EST removal was observed in the ASP when SRT increased from 10 to 27d. However, batch studies identified an augmented biomass sorption capacity for the more hydrophobic estrogens E2 and EE2 at 27d, equivalent to an order of magnitude. The lack of influence on estrogen removal during pilot plant operation can be ascribed to their distribution within activated sludge being under equilibrium. Consequently, lower wastage of excess sludge inherent of long SRT operation counteracts any improvement in sorption.

Quantifying the loss of methane through secondary gas mass transport (or 'slip') from a micro-porous membrane contactor applied to biogas upgrading.

Secondary gas transport during the separation of a binary gas with a micro-porous hollow fibre membrane contactor (HMFC) has been studied for biogas upgrading. In this application, the loss or 'slip' of the secondary gas (methane) during separation is a known concern, specifically since methane possesses the intrinsic calorific value. Deionised (DI) water was initially used as the physical solvent. Under these conditions, carbon dioxide (CO2) and methane (CH4) absorption were dependent upon liquid velocity (V(L)). Whilst the highest CO2 flux was recorded at high V(L), selectivity towards CO2 declined due to low residence times and a diminished gas-side partial pressure, and resulted in slip of approximately 5.2% of the inlet methane. Sodium hydroxide was subsequently used as a comparative chemical absorption solvent. Under these conditions, CO2 mass transfer increased by increasing gas velocity (VG) which is attributed to the excess of reactive hydroxide ions present in the solvent, and the fast conversion of dissolved CO2 to carbonate species reinitiating the concentration gradient at the gas-liquid interface. At high gas velocities, CH4 slip was reduced to 0.1% under chemical conditions. Methane slip is therefore dependent upon whether the process is gas phase or liquid phase controlled, since methane mass transport can be adequately described by Henry's law within both physical and chemical solvents. The addition of an electrolyte was found to further retard CH4 absorption via the salting out effect. However, their applicability to physical solvents is limited since electrolytic concentration similarly impinges upon the solvents' capacity for CO2. This study illustrates the significance of secondary gas mass transport, and furthermore demonstrates that gas-phase controlled systems are recommended where greater selectivity is required.

Fate and impact of organics in an immersed membrane bioreactor applied to brine denitrification and ion exchange regeneration.

The application of membrane bioreactors (MBRs) to brine denitrification for ion exchange regeneration has been studied. The developed culture was capable of complete brine denitrification at 50 gNaCl.l(-1). Denitrification reduced to c.60% and c.70% when salinity was respectively increased to 75 and 100g.l(-1), presumed to be due to reduced growth rate and the low imposed solids retention time (10 days). Polysaccharide secretion was not induced by stressed cells following salt shocking, implying that cell lysis did not occur. Fouling propensity, monitored by critical flux, was steady at 12-15l.m(-2).h(-1) during salinity shocking and after brine recirculation, indicating that the system was stable following perturbation. Low molecular weight polysaccharide physically adsorbed onto the nitrate selective anion exchange resin during regeneration reducing exchange capacity by c.6.5% when operating up to complete exhaustion. However, based on a breakthrough threshold of 10 mgNO(3)(-)-N.l(-1) the exchange capacity was comparative to that determined when using freshly produced brine for regeneration. It was concluded that a denitrification MBR was an appropriate technology for IEX spent brine recovery and reuse.

Removal of steroid estrogens in carbonaceous and nitrifying activated sludge processes.

A carbonaceous (heterotrophic) activated sludge process (ASP), nitrifying ASP and a nitrifying/denitrifying ASP have been studied to examine the role of process type in steroid estrogen removal. Biodegradation efficiencies for total steroid estrogens (Sigma(EST)) of 80 and 91% were recorded for the nitrifying/denitrifying ASP and nitrifying ASP respectively. Total estrogen biodegradation (Sigma(EST)) was only 51% at the carbonaceous ASP, however, the extent of biodegradation in the absence of nitrification clearly indicates the important role of heterotrophs in steroid estrogen removal. The low removal efficiency did not correlate with biomass activity for which the ASP(carbonaceous) recorded 80 microg kg(-1) biomass d(-1) compared to 61 and 15 microg kg(-1) biomass d(-1) at the ASP(nitrifying) and ASP(nitrifying/denitrifying) respectively. This finding was explained by a moderate correlation (r(2)=0.55) between total estrogen loading (Sigma(EST) mgm(-3)d(-1)) and biomass activity (microg Sigma(EST) degraded kg(-1) d(-1)) and has established the impact of loading on steroid estrogen removal at full-scale. At higher solids retention time (SRT), steroid estrogen biodegradation of>80% was observed, as has previously been reported. It is postulated that hydraulic retention time (HRT) is as important as SRT as this governs both reaction time and loading. This observation is based on the high specific estrogen activity determined at the ASP(carbonaceous) plant, the significance of estrogen loading and the positive linear correlation between SRT and HRT.