Modelling the performance of an integrated fixed-film activated sludge (IFAS) system: a systematic approach to automated calibration.

IFAS systems are inherently complex due to the hybrid use of both suspended and attached bacterial colonies for the purpose of pollutant degradation as part of wastewater treatment. This poses challenges when attempting to represent these systems mathematically due to the vast number of parameters involved. Besides becoming convoluted, large effort will be incurred during model calibration. This paper demonstrates a systematic approach to calibration of an IFAS process model that incorporates two sensitivity analyses to identify influential parameters and detect collinearity from a subset of 68 kinetic and stoichiometric parameters, and the use of the Nelder-Mead optimization algorithm to estimate the required values of these parameters. The model considers the removal of three critical pollutants including biochemical oxygen demand (BOD), total nitrogen (TN) and total suspended solids (TSS). Results from the sensitivity analyses identified four parameters that were the primary influence on the model. The model was found to be most sensitive to the two stoichiometric parameters including aerobic heterotrophic yield on soluble substrate whose total effects were responsible for 92.4% of the model's BOD output sensitivity and 92.8% of the model's TSS output sensitivity. The anoxic heterotrophic yield on soluble substrate was observed to be responsible for 54.3% of the model's TN output sensitivity. To a lesser extent the two kinetic parameters, aerobic heterotrophic decay rate and reduction factor for denitrification on nitrite, were responsible for only 8.0% and 13.1% of the model's BOD and TN output sensitivities respectively. Parameter estimation identified the need for only minor adjustments to default values in order to achieve sufficient accuracy of simulation with deviation from observed data to be only ± 3.6 mg/L, ± 1.3 mg/L, and ± 9.5 mg/L for BOD, TN and TSS respectively. Validation showed the model was limited in its capacity to predict system behaviour under extreme dissolved oxygen stress.

Predicting failures in electronic water taps in rural sub-Saharan African communities: an LSTM-based approach.

There is a growing need to sustain solar-powered water taps in most parts of the sub-Saharan Africa. The frequent failure of the water taps gives rise to intermittent water supply and poor service delivery by the water service providers. The challenge is to foresee and predict the failure of these water systems before they occur. This study develops a scalable machine-learning model for failure prediction in electronic water taps to ensure timely maintenance of the taps. Specifically, we develop a model based on long short-term memory (LSTM) to efficiently make failure predictions with noisy heterogeneous time-series data from rural water taps. Results from the experiment prove that the proposed model can effectively classify activities and patterns in various time-series datasets. With the proposed model, the failures of the solar-powered taps due to abnormal events can be successfully predicted well in advance, with an accuracy of 78.54%. Based on the data analyses, common causes of failures are presented.

Performance evaluation of conventional and water saving taps.

The rapid pace of urbanisation comes with considerable environmental implications including pressures on already stressed limited water resources. In urban areas, most of the water use is associated with water consumption in buildings. The second largest use of water is via taps. It is often assumed that water taps with low flow rates can contribute to reduced per capita water consumption. However, this is based on very little evidence. This paper presents the synthesis of a 13,000 high resolution observations made to investigate the actual water consumption of innovative (water saving) electronic taps and conventional mixer taps. High resolution flow-meters and data loggers were fitted into two washrooms in two different buildings of a higher education institution to record the water use through the basin taps. The recorded data provided information on duration, frequency of use and volume of water consumption per use. The data was helpful in identifying trends in hot and cold water use and therefore can be useful in estimating energy for producing hot water and associated greenhouse gas emissions. Analysis of the observed data suggests that the low flow taps have greater mean water consumption per event than the conventional taps and water consumption is more influenced by user behaviour rather than the technology.

Performance of a large building rainwater harvesting system.

Rainwater harvesting is increasingly becoming an integral part of the sustainable water management toolkit. Despite a plethora of studies modelling the feasibility of the utilisation of rainwater harvesting (RWH) systems in particular contexts, there remains a significant gap in knowledge in relation to detailed empirical assessments of performance. Domestic systems have been investigated to a limited degree in the literature, including in the UK, but there are few recent longitudinal studies of larger non-domestic systems. Additionally, there are few studies comparing estimated and actual performance. This paper presents the results of a longitudinal empirical performance assessment of a non-domestic RWH system located in an office building in the UK. Furthermore, it compares actual performance with the estimated performance based on two methods recommended by the British Standards Institute - the Intermediate (simple calculations) and Detailed (simulation-based) Approaches. Results highlight that the average measured water saving efficiency (amount of mains water saved) of the office-based RWH system was 87% across an 8-month period, due to the system being over-sized for the actual occupancy level. Consequently, a similar level of performance could have been achieved using a smaller-sized tank. Estimated cost savings resulted in capital payback periods of 11 and 6 years for the actual over-sized tank and the smaller optimised tank, respectively. However, more detailed cost data on maintenance and operation is required to perform whole life cost analyses. These findings indicate that office-scale RWH systems potentially offer significant water and cost savings. They also emphasise the importance of monitoring data and that a transition to the use of Detailed Approaches (particularly in the UK) is required to (a) minimise over-sizing of storage tanks and (b) build confidence in RWH system performance.

Environmental implications of water efficient microcomponents in residential buildings.

The Code for Sustainable Homes (CSH) in England sets out various water efficiency targets/levels, which form part of environmental performance criteria against which the sustainability of a building is measured. The code is performance based and requires reduction in per capita water consumption in households. The water efficiency related targets can be met using a range of water efficient microcomponents (WC, showers, kitchen taps, basin taps, dishwashers, washing machines, and baths). However, while the CSH aims at reducing the adverse environmental implications associated with the dwellings by promoting reduction in water consumption, little is known about the energy consumption and the environmental impacts (e. g. carbon emissions) resulting from water efficient end uses. This paper describes a methodology to evaluate the energy consumption and carbon emissions associated with the CSH's water efficiency levels. Key findings are that some 96% and 87% of energy use and carbon emissions, respectively associated with urban water provision are attributable to in-house consumption (principally related to hot water), and that achieving a defined water efficiency target does not automatically save energy or reduce carbon emissions.

Harvested rainwater quality: the importance of appropriate design.

This paper summarises the physicochemical and microbiological quality of water from a rainwater harvesting (RWH) system in a UK-based office building. 7 microbiological and 34 physicochemical parameters were analysed during an 8 month period. Physicochemically, harvested rainwater quality posed little health risk; most parameters showed concentrations below widely used guideline levels for drinking water. However, RWH system components (e.g. fittings and down pipes) appear to be affected soft water corrosion, resulting in high concentrations of some metals (copper, zinc and aluminium). This suggests the material selection of such fittings should be considered keeping in view the hardness of rainwater of an area. Microbiologically, Cryptosporidium, Salmonella and Legionella were not present in the samples analysed. However, faecal coliform counts were high at the beginning of the study, but did decrease over time in weak correlation with increasing pH. Enterococcus faecalis displayed counts consistently above UK rainwater harvesting standards. Inappropriate roof and rainwater good design, as well as material selection appear to be responsible for the reduced microbial quality, as they promoted contributions from avian sources and inhibited cleaning activities. Building and RWH system designs require greater consideration of local factors, which are critical for optimising harvested rainwater quality, to prevent both the development of contaminated sediments and health impacts.

Rainwater harvesting: model-based design evaluation.

The rate of uptake of rainwater harvesting (RWH) in the UK has been slow to date, but is expected to gain momentum in the near future. The designs of two different new-build rainwater harvesting systems, based on simple methods, are evaluated using three different design methods, including a continuous simulation modelling approach. The RWH systems are shown to fulfill 36% and 46% of WC demand. Financial analyses reveal that RWH systems within large commercial buildings maybe more financially viable than smaller domestic systems. It is identified that design methods based on simple approaches generate tank sizes substantially larger than the continuous simulation. Comparison of the actual tank sizes and those calculated using continuous simulation established that the tanks installed are oversized for their associated demand level and catchment size. Oversizing tanks can lead to excessive system capital costs, which currently hinders the uptake of systems. Furthermore, it is demonstrated that the catchment area size is often overlooked when designing UK-based RWH systems. With respect to these findings, a recommendation for a transition from the use of simple tools to continuous simulation models is made.

Impacts of residence time during storage on potential of water saving for grey water recycling system.

Grey water recycling has been generally accepted and is about to move into practice in terms of sustainable development. Previous research has revealed the bacteria re-growth in grey water and reclaimed municipal water during storage. However, in most present grey water recycling practices, impacts of water quality changes during storage on the system's performance and design regulation have not been addressed. In this paper, performance of a constructed wetland based grey water recycling system was analysed by taking the constraint of residence time during storage into account using an object based household water cycle model. Two indicators, water saving efficiency (WSE) and residence time index (RTI), are employed to reflect the system's performance and residence time during storage respectively. Results show that WSE and RTI change with storage tank volumes oppositely. As both high WSE and RTI cannot be achieved simultaneously, it is concluded that in order to achieve the most cost-effective and safe solution, systems with both small grey and green tanks are needed, whilst accepting that only relatively modest water saving efficiency targets can be achieved. Higher efficiencies will only be practicable if water quality deterioration in the green water tank can be prevented by some means (e.g. disinfection).

A framework for supporting rainwater harvesting in the UK.

Numerous policy vehicles have been introduced in the UK promoting the use of rainwater harvesting (RWH). However, an 'implementation deficit' exists where legislation limits action by failing to provide adequate support mechanisms. This study uses an interdisciplinary approach to construct a framework to address the issue of overcoming this deficit. Evidence bases have identified six deficit categories, which confirm a lack of enabling of stakeholders. Outline recommendations, such as coordinated information provision and reconsideration of incentive schemes are made in relation to these categories to complete the framework for supporting RWH in the UK.

A performance investigation of small-bore sewers.

This paper describes a full-scale physical model and its application to investigate the effectiveness/performance of small-bore sewers for a range of operational and design parameters. The implementation methodology involves observing the movement of synthetic gross solids in three small bore sewers (150, 100 and 75 mm diameter) for different volumes of simulated flush waves and gradients. The simulated flush waves were generated, using an automated wave sequencer, for three different flush volumes (3, 4.5 and 6 litres). To investigate the impact of solid shape factor, a number of tests were carried out using synthetic solids in combination with toilet tissue paper. In total, more than 1,000 tests were performed for different operational and design parameter combinations. Results obtained to date have confirmed earlier studies, particularly with respect to the role of flush volume in solids transport, and identified the impact of gradient variation and its significance particularly in small-bore sewers receiving low flush volume. Results from the physical model application exercise will be used to propose new design guidelines for wastewater collection systems with specific consideration to new developments and inform the decision support system, currently being developed as part of a research project on water cycle management for new developments (WaND).

Life cycle impact assessment of greywater recycling technologies for new developments.

This paper presents the life cycle impact assessment (LCIA) of four treatment technologies currently under investigation for recycling the greywater generated from households and describes the development of a new LCIA tool set produced in this study. The technologies investigated include reed beds, membrane bioreactors (MBR); membrane chemical reactors (MCR) and an innovative green roof water recycling system (GROW). The materials and energy required for the construction and operation phases of these technologies have been quantified for 20 development scales. All of the information gathered is used to prepare life cycle inventories for each technology. The inventories have been used as an input to Simapro Software for performing LCIA. Two assessment methods (CML-2 and Eco-indc-99) have been employed. For the CML method, the results were processed to express the environmental performance in ten impact categories including climate change/global warming, depletion of abiotic resources, acidification, eutrophication, and human toxicity. For the Eco-indc-99 method, results are shown in three generic environmental indicators: human health, eco system and natural resources. LCIA results obtained for 20 development scales have been used to develop a tool set using adaptive neuro-fuzzy inference system technique. The study results indicate that the technologies based on natural treatment processes (GROW and reed beds) have low environmental impact.

A decision support framework for sustainable urban water planning and management in new urban areas.

The paper discusses issues of decision support within the context of sustainable development and more specifically sustainable water cycle management to provide a context and a rationale for the decision support approach adopted within an on-going U.K. EPSRC-funded project, WaND. The paper proposes a set-up for a flexible, upgradeable, efficient and modular decision support framework and associated tools. Furthermore, the paper presents early prototypes of three decision support tools developed within the proposed framework including initial results for one of them.

Life cycle assessment of wastewater treatment technologies treating petroleum process waters.

This paper describes the implementation of life cycle assessment to investigate the environmental impact of 20 technologies suitable for treating extensive volumes of water produced during the oil and gas extraction processes. Data on the physical and operational attributes of technologies under consideration were assembled and their life cycle environmental impacts estimated over 15 year time period. The results were then incorporated in a decision support system which allows identification and prioritisation of potential technology combinations capable of producing water for nine designated industrial and agricultural end uses. In total, more than 618 technology combinations were investigated for their environmental impacts. The identification and prioritisation of technologies were done on the basis of their environmental and technical performance. This analysis showed that dissolved air flotation, absorbents, dual media filtration and reverse osmosis technologies offer relatively low environmental impact parts of systems for cleaning such process waters. Furthermore, the environmental assessment combined within the decision support system has revealed potentially valuable indirect downstream "benefits" from effects such as evaporative losses from wetlands in terms of the overall environmental impact of a treatment system.

Assessment of gully pot management strategies for runoff quality control using a dynamic model.

A gully pot is the first entry point of road runoff into an urban drainage network. Pots are extensively used to trap solids from runoff in order to avoid/minimise the problems associated with sediment deposition in the downstream drainage structures or receiving waters. Here we briefly describe the different modules of a dynamic gully pot model developed to assess the impact of a series of management practice scenarios on the quality of runoff discharged through the pots. Runoff quality was modelled in terms of suspended solids (SS), chemical oxygen demand (COD), dissolved oxygen (DO) and ammonium. The model has the flexibility to represent the impact of various interactions between physical and biochemical processes occurring in a pot during wet and dry weather conditions, respectively. The simulation results show that the pots are effective at retaining solids, but their role with regard to reduction of dissolved pollutants is almost neutral. Model predictions, as against common perception, show that frequent pot cleaning does not significantly improve the runoff quality. However, considerably improved solid retention is possible if larger pots with modified geometry are introduced into the drainage system.

Identification and modelling of dry weather processes in gully pots.

This paper presents the results of a monitoring and modelling programme, carried out to study the processes occurring in gully pots during dry weather. The monitoring programme involved estimation of the change in gully pot liquor quality, under field and laboratory conditions. The contents (i.e. liquor and sludge) of pots draining five different types of roads were monitored over dry periods in the winter and summer. A bench scale study was carried out to study the influence of temperature variations and sludge digestion by-products on gully liquor quality. The change in quality was measured in terms of chemical oxygen demand (COD), dissolved oxygen (DO) and ammonium concentration. The trends for change in COD and DO, were found to be broadly similar for all road types. However, ammonium transformation was found to follow different patterns at different locations. Several dry weather processes, such as COD decay, ammonium transformation, oxygen depletion and uptake by sludge, oxygen transfer from the atmosphere and benthic release of COD, have been identified. Other processes, found to take place during dry weather, include development of a scum layer over the surface of the gully liquor and sludge bulking. A model is proposed which can predict the change in gully liquor quality in terms of COD, DO and ammonium concentrations. Data collected during the study has been used to successfully calibrate and verify the model.