Economic assessment tool for greywater recycling systems

The implementation of water demand management strategies, particularly in urban environments, can contribute towards improved sustainability (or at least reduce unsustainability) in the water sector. Greywater treatment, and its subsequent use for toilet flushing, is one of the demand management options offering considerable water-saving potential. The uptake of greywater recycling systems (GRSs), particularly in the UK, is low. One of the reasons for such a low uptake is the perception that GRSs have a high (unsustainable) cost/benefit ratio. This paper presents progress on the development of a whole-life cost (WLC) model, aimed at facilitating decision making for the implementation of GRSs in relation to their economic viability

Transitioning from electrodialysis to reverse electrodialysis stack design for energy generation from high concentration salinity gradients

In this study, stack design for high concentration gradient reverse electrodialysis operating in recycle is addressed. High concentration gradients introduce complex transport phenomena, which are exacerbated when recycling feeds; a strategy employed to improve system level energy efficiency. This unique challenge indicates that membrane properties and spacer thickness requirements may differ considerably from reverse electrodialysis for lower concentration gradients (e.g. seawater/river water), drawing closer parallels to electrodialysis stack design. Consequently, commercially available electrodialysis and reverse electrodialysis stack design was first compared for power generation from high concentration gradients. Higher gross power densities were identified for the reverse electrodialysis stack, due to the use of thinner membranes characterised by a higher permselectivity, which improved current. However, energy efficiency of the electrodialysis stack was twice that recorded for the reverse electrodialysis stack at low current densities, which was attributed to: (i) an increased residence time provided by the larger intermembrane distance, and (ii) reduced exergy losses of the electrodialysis membranes, which provided comparatively lower water permeance. Further in-depth investigation into membrane properties and spacer thickness identified that membranes characterised by an intermediate water permeability and ohmic resistance provided the highest power density and energy efficiency (Neosepta ACS/CMS), while wider intermembrane distances up to 0.3 mm improved energy efficiency. This study confirms that reverse electrodialysis stacks for high concentration gradients in recycle therefore demand design more comparable to electrodialysis stacks to drive energy efficiency, but when selecting membrane properties, the trade-off with permselectivity must also be considered to ensure economic viability

Hybrid membrane distillation reverse electrodialysis configuration for water and energy recovery from human urine: an opportunity for off-grid decentralised sanitation

The integration of membrane distillation with reverse electrodialysis has been investigated as a sustainable sanitation solution to provide clean water and electrical power from urine and waste heat. Reverse electrodialysis was integrated to provide the partial remixing of the concentrate (urine) and diluate (permeate) produced from the membrane distillation of urine. Broadly comparable power densities to those of a model salt solution (sodium chloride) were determined during evaluation of the individual and combined contribution of the various monovalent and multivalent inorganic and organic salt constituents in urine. Power densities were improved through raising feed-side temperature and increasing concentration in the concentrate, without observation of limiting behaviour imposed by non-ideal salt and water transport. A further unique contribution of this application is the limited volume of salt concentrate available, which demanded brine recycling to maximise energy recovery analogous to a battery, operating in a ‘state of charge’. During recycle, around 47% of the Gibbs free energy was recoverable with up to 80% of the energy extractable before the concentration difference between the two solutions was halfway towards equilibrium which implies that energy recovery can be optimised with limited effect on permeate quality. This study has provided the first successful demonstration of an integrated MD-RED system for energy recovery from a limited resource, and evidences that the recovered power is sufficient to operate a range of low current fluid pumping technologies that could help deliver off-grid sanitation and clean water recovery at single household scale

Anaerobic membrane bioreactors enable high rate treatment of slaughterhouse wastewater

Anaerobic membrane bioreactors (AnMBRs) enable high space loading by retaining solids selectively through microfiltration membranes. For organic industrial wastewaters, this offers an alternative to lagoons and granule based high-rate anaerobic treatment due to excellent effluent quality, high tolerance to load variations, and ability to produce a solids free effluent for the purposes of reuse. While there has been extensive work on low-strength and low solids effluent, there has been limited application in high-solids, high fats systems such as slaughterhouse wastewater, which are a key application. A 200L AnMBR pilot plant operated at 2 Australian cattle slaughterhouses consistently removed over 95% of chemical oxygen demand (COD) from the wastewater. Virtually all degradable COD was converted to biogas, 78-90% of nitrogen and 74% of phosphorus in the wastewater were released to the treated permeate as ammonia and phosphate, respectively; which would enable subsequent nutrient capture. The mass loading rate limit of 3-3.5g CODLd is imposed by the active biomass inventory, with this in turn limited to 40gL (TS) by the need to manage membrane fouling control

Managing power dissipation in closed-loop reverse electrodialysis to maximise energy recovery during thermal-to-electric conversion

Whilst the efficiency of reverse electrodialysis (RED) for thermal-to-electrical conversion has been theoretically demonstrated for low-grade waste heat, the specific configuration and salinity required to manage power generation has been less well described. This study demonstrates that operating RED by recycling feed solutions provides the most suitable configuration for energy recovery from a fixed solution volume, providing a minimum unitary cost for energy production. For a fixed membrane area, recycling feeds achieves energy efficiency seven times higher than single pass (conventional operation), and with an improved power density. However, ionic transport, water flux and concentration polarisation introduce complex temporal effects when concentrated brines are recirculated, that are not ordinarily encountered in single pass systems. Regeneration of the concentration gradient at around 80% energy dissipation was deemed most economically pragmatic, due to the increased resistance to mass transport beyond this threshold. However, this leads to significant exergy destruction that could be improved by interventions to better control ionic build up in the dilute feed. Further improvements to energy efficiency were fostered through optimising current density for each brine concentration independently. Whilst energy efficiency was greatest at lower brine concentrations, the work produced from a fixed volume of feed solution was greatest at higher saline concentrations. Since the thermal-to-electrical conversion proposed is governed by volumetric heat utilisation (distillation to reset the concentration gradient), higher brine concentrations are therefore recommended to improve total system efficiency. Importantly, this study provides new evidence for the configuration and boundary conditions required to realise RED as a practical solution for application to sources of low-grade waste heat in industr

Membrane-assisted reactive crystallisation for the recovery of dissolved phosphorus in vivianite form from liquid effluents

Novel membrane crystallisation processes resolve the mixing challenge on conventional crystallisers, by providing fixed interfacial area over which supersaturation is controlled for nucleation. Moreover, the membrane surface is thought to reduce interfacial energy and encourage micromixing. In this regard, a novel membraneassisted reactive crystallisation (MARC) process was used in this work for the dissolved phosphorous recovery in form of vivianite crystals from a phosphate-rich solution by means of the dosing of iron (II). To characterise the role of the boundary layer in controlling nucleation, a batch lab-scale system was used for the crystallization tests, and different hydraulic conditions (Reynolds ranging from 105 to 395) and polymeric membranes were tested. The crystallisation process was influenced by the hydraulic conditions, in which a low liquid velocity led to a lower induction time and vivianite supersaturation, and therefore, higher nucleation rates. Membrane properties were characterised to establish their role in the modification of the critical free energy requirement for nucleation, and for the promotion of micromixing, as possible factors that can be used to modify nucleation kinetics. As result, the bulk induction time tended to decrease with the increase in membrane hydrophobicity, roughness, pore size and porosity. Spherical vivianite nanoparticles were always synthesised with a mean size around 35 nm and a narrow distribution independently of the hydraulic conditions and membrane used. Finally, the crystallisation kinetic conformed to a diffusion-dependent nucleation mechanism, in which higher residence times for mixing increased the ion collision probability for nucleation. Importantly, this study demonstrated that MARC is an attractive prospect for nutrient recovery from wastewaters where crystal nucleation can be easily controlled by setting the operational conditions and membrane properties, eliciting considerable process intensification over existing conventional crystalliser.European Union funding: 71408

Quantification of liquid phase faecal odourants to evaluate membrane technology for wastewater reuse from decentralised sanitation facilities

Public willingness to use decentralised sanitation facilities or arising water products is discouraged due to malodour, preventing improved sanitation practices or water reuse opportunities in low income countries. Whilst odour is characterised in the gas phase, it originates in the liquid phase. Consequently, controlling odour at source could prevent gas-phase partitioning and limit produced water contamination. This study therefore developed an analytical method for the quantitation of a range of liquid phase volatile organic compounds (VOCs) classified into eight chemical groups, known to be primary indicators of faecal odour, to provide characterisation of real fluids and to permit evaluation of several potential membrane separation technologies for liquid phase odourant separation. The gas chromatography mass spectrometry method provided quantitation in the range of 0.005 mg L−1 to 100 mg L−1 with instrument detection limits ranging from 0.005 mg L−1 to 0.124 mg L−1. Linear calibration curves were achieved (r2 > 0.99) with acceptable accuracy (77-115%) and precision (<15%) for quantitation in the calibration range below 1 mg L−1, and good accuracy (98-104%) and precision (<2%) determined for calibration in the range 1-100 mg L−1. Pre-concentration of real samples was facilitated via solid phase extraction. Subsequent application of the method to the evaluation of two thermally driven membranes based on hydrophilic (polyvinyl alcohol) and hydrophobic (polydimethylsiloxane) polymers evidenced contrasting separation profiles. Importantly, this study demonstrates the method's utility for liquid phase VOC determination which is of use to a range of disciplines, including healthcare professionals, taste and odour specialists and public health engineers

Greywater recycling: Treatment options and applications

Wastewater is an immense resource that could find significant applications in regions of water scarcity. Greywater has particular advantages in that it is a large source with a low organic content. Through critical analysis of data from existing greywater recycling applications, this paper presents a review of existing technologies and applications by collating a disparate information base and comparing/contrasting the strengths and weaknesses of different approaches. Simple technologies and sand filters have been shown to have a limited effect on greywater; membranes are reported to provide good solids removal but cannot efficiently tackle the organic fraction. Alternatively, biological and extensive schemes achieve a good general treatment of greywater with particularly effective removal of organics. The best overall performances were observed within schemes that combine different types of methods to ensure effective treatment of all the fractions

Financial feasibility of end-user designed rainwater harvesting and greywater reuse systems for high water use households

© 2017, The Author(s). Water availability pressures, competing end-uses and sewers at capacity are all drivers for change in urban water management. Rainwater harvesting (RWH) and greywater reuse (GWR) systems constitute alternatives to reduce drinking water usage and in the case of RWH, reduce roof runoff entering sewers. Despite the increasing popularity of installations in commercial buildings, RWH and GWR technologies at a household scale have proved less popular, across a range of global contexts. For systems designed from the top-down, this is often due to the lack of a favourable cost-benefit (where subsidies are unavailable), though few studies have focused on performing full capital and operational financial assessments, particularly in high water consumption households. Using a bottom-up design approach, based on a questionnaire survey with 35 households in a residential complex in Bucaramanga, Colombia, this article considers the initial financial feasibility of three RWH and GWR system configurations proposed for high water using households (equivalent to >203L per capita per day). A full capital and operational financial assessment was performed at a more detailed level for the most viable design using historic rainfall data. For the selected configuration (‘Alt 2’), the estimated potable water saving was 44% (equivalent to 131m3/year) with a rate of return on investment of 6.5% and an estimated payback period of 23years. As an initial end-user-driven design exercise, these results are promising and constitute a starting point for facilitating such approaches to urban water management at the household scale

EURECOM at TRECVID 2016. The Adhoc Video Search and Video Hyperlinking Tasks

Contains fulltext : 166346.pdf (publisher's version ) (Open Access)TRECVID 2016, 14 november 201