An experiment with a plastic solar still

A solar still is a device which allows obtaining fresh water from seawater or brackish water. It utilizes the greenhouse effect by using solar energy. In a conventional solar still the production of fresh water in bright sunny weather and with warm air temperature is about 5-5.5 L m⁻² d⁻¹, according to the depth of the water in the solar still. In some devices it is possible to obtain efficiencies of up to 0.50 and 0.60. The aim of this research is to increase distillation productivity by utilizing the latent heat released by the condensing water steam. For this purpose the author built a solar still characterized by two basins (B₁ and B₂) superimposed upon each other. The building materials were a sheet of black Plexiglas for the bottom of the solar still, a sheet of transparent Plexiglas for all boxes, and a sheet of expanded polystyrene, used as insulating material. The solar still was hermetically sealed to reduce the leakage of vapor to the surroundings. The greatest quantity of fresh water obtained by the tested solar still was 1.7-1.8 L m⁻² d⁻¹. This result was achieved in the third week of July when solar radiation was 27-28 MJ m⁻² d⁻¹. The efficiency of the tested solar still was about 0.16. This low efficiency is probably due to the low temperature of the water contained in the still (about 50°C). The solar still has only been used in experiments for some months, during which it has not been possible to study the deterioration of the material (Plexiglas). These results show that an elaborate design and the increased costs for such design and construction do not always improve the water yield.     

Process development and modeling of pyruvate recovery from a model solution and fermentation broth

The mono- and bi-polar electrodialysis processes for pyruvate recovery and pyruvic acid generation, respectively, were examined in order to determine their feasibility for application in the pyruvate production process. Under optimum process conditions (constant current mode i = 39.7 A m⁻², pyruvate model solution c_p = 50 g dm⁻³ in the monopolar electrodialysis experiment pyruvate flux reached 367 g m⁻² h⁻¹ and specific energy consumption was 1.4 kWh kg⁻¹. In the bi-polar electrodialysis experiment under optimum process conditions (constant current mode i = 9.6 A m⁻², pyruvate model solution c_p = 48 g dm⁻³, pyruvate flux reached 125 g m⁻² h⁻¹ and specific energy consumption was 1.5 kWh kg^-1. Generally speaking, performances of the bi-polar electrodialysis were equal to the best process conditions observed with mono-polar electrodialysis. On the other hand, current densities investigated in the bi-polar electrodialysis experiments were four-fold lower than those applied in the mono-polar electrodialysis experiments. Additionally, a mathematical model to represent the ion and water transport behavior of an electrodialysis process for concentrating pyruvic acid under the influence of different current density was developed. Estimation of both the model parameters and model validation were demonstrated in the work.     

Seawater reverse osmosis with energy recovery

The Porto Santo seawater reverse osmosis plant has been designed to provide per day 500 m³ of potable water with a total dissolved solids content of 500 ppm from seawater with a total dissolved solids content of abt. 34000 ppm.The plant consists of four independent units with an output of 125 m³ per day each. Three units are fed by high pressure pumps equipped with electro-motors and one unit by a high pressure pump equipped with a hydro-turbine. The high pressure reject stream from each unit is directed into a manifold pipe which powers the hydro-turbine. In this way power consumption of the high pressure pump is reduced by 25 percent. Without energy recovery consumption would have been 7.5 kWh/m³ and with the installed turbine this is as low as 5.6 kWh/m³ of product.     

Phosphorus recovery from centralised municipal water recycling plants

Depletion of world phosphorus reserves is driving research into options to recover and recycle this essential, non-renewable resource. Phosphate (PO₄³⁻) recovery at centralised wastewater treatment plants can be achieved through biosolids reuse or sidestream precipitation though the PO₄³⁻ levels are low compared with decentralised systems based on source separation. However, the recent growth in membrane based water recycling projects, where reverse osmosis is used to produce high quality water has resulted in the production of liquid waste streams with elevated concentrations of PO₄³⁻. Four recycling scenarios using different membrane processes and anaerobic treatment were compared and the potential PO₄³⁻ recovery via struvite (magnesium ammonium phosphate) from membrane concentrate examined. By incorporating an anaerobic reactor in the process we have been able to investigate the possibility of cogeneration of electricity from methane. Modelling of struvite recovery from membrane concentrate with co-generation indicates a net power requirement of 260 kWh/kg P recovered compared with 510 kWh/kg P for a system without cogeneration at a water consumption level of 250 L/p/d. When water consumption is limited to 80 L/p/d, this scenario compares favourably with literature values for recovery from source separated urine which range from 18 to 43 kWh/kg P.     

Piezoelectric cement-based materials with large coupling and voltage coefficients

Cement paste containing short steel fibers (8 μm diameter, 0.18 vol.%) and polyvinyl alcohol (0.16 vol.%) exhibits longitudinal piezoelectric coupling coefficient d=2.5×10⁻¹¹ m/V and piezoelectric voltage coefficient g=1.1×10⁻³ m²/C (10 kHz), compared to values of d=3.0×10⁻¹³ m/V and g=1.1×10⁻³ m²/C for cement paste without admixture, and values of d=1.4×10⁻¹¹ m/V and g=1.5×10⁻³ m²/C for lead zirconotitanate (PZT).     

Feasibility studies of discontinuous electro-regeneration processes in environmentally-friendly plating for chromate separation from a binary system

Project work was carried out for feasibility and possible design of semi-industrial electro-regeneration units for diluted waters typical for rinse water systems in electroplating industry. Firstly, one subject of interest was the removal of CrO₄²⁻ ions in the concentration range between 0.06 mol m⁻³ and 2.3 mol m⁻³. Ion exchange capacity of several resins under room temperature conditions was tested. A 2-compartment cell with diaphragm was found to be a suitable construction for electrochemical resin regeneration after previous discontinuous loading. The determination of resin conductivities and transport numbers was also part of the studies. Results showed sufficient high current efficiencies up to 70%. Nevertheless, low ion mobility in the resin may limit the removal rate for continuous electrodeionization. In this case, stepwise operation mode in loading and regenerating the resin bed is the only solution. Energy consumption can be lowered by using catholytes of previous electro-regeneration steps. Specific energy consumption until 0.3 kWh per treated cubic meter is to be expected.     

Experiences on greywater re-use for toilet flushing in a hotel (Mallorca Island, Spain)

An indoor greywater recycling system to flush the toilets in a hotel is described. The system is based on filtration, sedimentation and disinfection treatments using hypochlorite as the disinfecting agent. An average amount of water of 5.2 m³/d⁻¹ was re-used, which represents 23% of the total water consumption of the hotel. A moderate hypochlorite dose (75 mg chlorine l⁻¹) and a controlled residence time (<48 h) led to a residual chlorine concentration at cistern toilets higher than 1 mg l⁻¹. Under such conditions, all samples were negative for total coliform bacteria. A maintenance program was proposed and an economics assessment was also reported. Customer acceptance was clearly satisfactory. This is the first paper reporting data on greywater reuse for toilet flushing in a hotel.     

Effect of limited artificial aeration on constructed wetland treatment of domestic wastewater

To study the effect of limited artificial aeration on domestic wastewater treatment in the constructed wetlands (CWs), four pilot-scale horizontal subsurface flow CWs were operated from October 2006 to September 2007. The types of the four units include aerated and planted CW (APCW), planted CW (PCW), aerated CW (ACW) and CW, and all the units have the identical dimensions of 3 m in length, 0.7 m in width and 1 m in depth. The automated aeration was activated when the oxygen concentrations in the units were lower than 0.2 mg/L and ceased when the oxygen concentrations in the CWs were higher than 0.6 mg/L. More stable alkaline pH values were found in aeration units than that in the non-aeration units. APCW, in which the removal efficiencies of BOD, NH₄⁺-N and TN were 94.4% (16.7 g BOD d^− 1 m^− 2), 89.1% (4.54 g NH₄⁺-N d^− 1 m^− 2), and 86.0%( 4.99 g TN d^− 1 m^− 2) respectively, was more effective at pollutant removal than the other three units. There were no significant differences in TP removal between the aeration units and non-aeration units. Less surface area is needed due to high removal efficiency in APCW and the additional cost of operation is quite little. The results from this experiment indicated that limited artificial aeration in constructed wetlands is a cost-effective method for treating domestic wastewater.     

An exergetic analysis of a membrane desalination system

In this paper, the exergetic analysis of a seawater membrane-based desalination plant has been carried out. The desalination plant has been described in detail, then the exergy of the various saline water streams has been determined and a comprehensive analysis towards the exergy distribution of the major process components has been conducted. The examination of the exergy losses throughout the plant revealed that exergy destruction was mainly due to pressure drops in the membrane modules, valves and brine lines. Moreover, 12.9% of the exergy input to the system was supplied by the heater. Therefore, the most reasonable way to reduce power input to the plant, thus improving its performance and cost, has been shown (i) to be replacing the valves on the reverse osmosis brine stream by an energy recovery system, and (ii) to have thermal energy available in the plant. With the identified technical changes, energy consumption decreased from 18.3 to 2.05 kWh/m³, resulting in an annual saving of 0.17$/m³.     

Biological and electrochemical oxidation of naphthalenesulfonates

A biofilm airlift suspension (BAS) reactor and an undivided flow cell equipped with a boron‐doped diamond (BDD) anode and a stainless‐steel cathode were used to investigate the effects of varying operating conditions on process performance in the biological and electrochemical oxidation of a mixture of naphthalenesulfonates contained in the infiltration water of a contaminated industrial site. The experiments were aimed at evaluating the feasibility of process integration and the criteria for optimization (i.e. how to maximize degradation efficiency with minimum energy consumption) in combined biological and electrochemical oxidation of scarcely biodegradable compounds. Because of high reactor biomass concentration and long biomass retention time, the BAS reactor achieved a high degradation capacity (up to 6.8 kg COD m^?3 d^?1). On the other hand, owing to the recalcitrant character of some of the aromatic sulfonates in the leachate, the overall degradation efficiency did not exceed 70% based on COD measurements. All naphthalene‐mono‐ and ‐disulfonates (except naphthalene‐1,5‐disulfonate) were completely degraded in the BAS reactor, whereas more complex molecules (e.g. naphthalenetrisulfonates) were more recalcitrant to biological oxidation. These compounds were completely mineralized by electrochemical oxidation using a boron‐doped diamond anode. The energy consumption and the time required for the complete mineralization of the infiltration water decreased from 80 kWh m^?3 and 4 h to 61 kWh m^?3 and 3 h for the oxidation of raw and biologically pretreated leachate, respectively. Copyright © 2005 Society of Chemical Industry     

Cathodic Decolourisation of Dyes in Concentrates from Nanofiltration and Printing Pastes

Direct cathodic reduction of dyes which contain an azo-goup in the chromophore was successfully used for decolourisation of intensively coloured concentrates from Nanofiltration treatment of textile effluents. Based on laboratory scale experiments, a technical multi-cathode electrolyser was applied for full scale decolourisation experiments at cell currents from 40 to 80 A. The absorbance of the treated wastes decreased from 60 to 80% of the initial value at an energy consumption of 2–8 kWh m^–3. Experiments with addition of redox mediator indicate a significant increase in decolourisation rate; however chemical consumption is increased for 0.5–1.5 kg m^–3 of waste. The decolourisation of reactive dye containing printing pastes was also achieved at the laboratory scale, where decolourisation of 60–80% was achieved.     

Flat-plate submerged membrane bioreactor for the treatment of higher-load graywater

Graywater treatment has been the focus when topics of decentralized treatment systems are discussed. In this paper, the treatment of higher-load graywater, a mixture of washing machine and kitchen sink wastewater, was investigated. A 10 L lab-scale submerged membrane bioreactor (subMBR) was operated with a flat-plate membrane for 87 days. Permeate was intermittently withdrawn at constant transmembrane pressure (TMP) induced by water level difference and without pump requirement. The pollutants' removal and membrane behavior were monitored. The COD removal was around 96% and a permeate COD of about 26 mg L^− 1 was obtained. The total linear alkylbenzene sulfonate (LAS) removal achieved was > 99%, indicative of its non-inhibited degradation even at influent concentration of 30.8 mg L^− 1. The subMBR was operated at almost stable and constant flux of 0.22 m³ m^− 2 d^− 1 at a mean HRT of 13.6 h.     

Bilge Water Treatment in an Upflow Electrochemical Reactor using Pt Anode

Bilge water treatment was studied in an upflow electrochemical reactor (UECR) in order to design a compact onboard wastewater treatment system. The influence of retention time on the removal efficiencies of chemical oxygen demand (COD) and turbidity were analyzed, and optimized using response surface methodology (RSM) for maximizing the removal efficiencies. The best operating performance was obtained at 390 min retention time and 480 min reaction time for cost effective analysis with the composition of 100% bilge water (COD_o = 3080 mg/L) and 50/50% seawater/fresh water, 12.8 mA/cm² current density, and 32°C reaction temperature. Under response surface optimized conditions, the responses were estimated as; 90% COD removal, 97% turbidity removal, outlet pH value of 8.1, mass transfer coefficient of 0.494 × 10^?5 m/s, and mean energy consumption of 44.8 kWh/kg COD removed.     

Artificial intelligence for greywater treatment using electrocoagulation process

Treatment of greywater by electrocoagulation using aluminum electrodes was studied. The effects of current-density, electrolysis-time, and inter-electrode-gap on turbidity-removal and electrical-energy consumption were investigated. Under the optimal conditions (J = 12.5 mA/cm², t = 30 min, and l = 0.5 cm), pollutants removal were: COD_total = 52.8%, COD_soluble = 31.4%, BOD_total = 32.8%, BOD_soluble = 27.6%, SS = 64.6%, TN = 30.1%, and TP = 13.6%. The consumed electrical-energy recorded 4.1 kWh/m³ with an operating cost 0.25 US $/m³. Artificial intelligence was developed to simulate the influence of variables on the turbidity-removal. A 3–6–1 neural network achieved R-values: 0.99 (training), 0.84 (validation) and 0.89 (testing). An adaptive neuro-fuzzy inference system indicated that current-density is the most influential input.     

Performance of the hydrolyzation film bed and biological aerated filter (HFB–BAF) combined system for the treatment of low‐concentration domestic sewage in south China

The performance of the hydrolyzation film bed and biological aerated filter (HFB–BAF) combined system in pilot scale (with a daily treatment quantity of 600–1300 m³ d^?1), operated for 234 days, for low‐strength domestic sewage was assessed using different amounts of aeration, reflux ratios and hydraulic loading rates (HLR). In steady state it was found that the average removal efficiency of chemical oxygen demand (COD) and biological oxygen demand at 5 days (BOD₅) were 82.0% and 82.2% and the average effluent concentrations were 15.8 mg L^?1 and 9.4 mg L^?1 respectively as the HFB was running at an HLR of 1.25–1.77 m³ m^?2 h^?1 and the BAF was running at an HLR of 1.56–2.21 m³ m^?2 h^?1. In general, the removal efficiency of total nitrogen (TN) fluctuated with the HLR, gas–water ratio and reflux ratio, so the ratio of gas to water should be controlled from 2:1 to 3:1 and the reflux ratio should be as high as possible. The effluent concentration of TN was 10.4 mg L^?1 and the TN removal averaged 34.3% when the gas–water ratio was greater than 3:1 and the reflux ratio was 0.5. The effluent concentration and removal efficiency of NH₄⁺‐N averaged respectively 2.3 mg L^?1 and 78.5%. The overall reduction of total phosphorus (TP) was 30% and the average effluent concentration was 0.95 mg L^?1. The removal efficiency of linear alkylbenzene sulfonates (LAS) reached 83.8% and the average effluent concentration was almost 0.9 mg L^?1. The effluent concentration and removal efficiency of polychlorinated biphenyls (PCBs) were 0.0654 µ g L^?1 and 37.05% respectively when the influent concentration was 0.1039 µ g L^?1. The excess sludge containing water (volume 15 m³) was discharged once every 3 months. The power consumption of aeration was 0.06–0.09 kWh of sewage treated. The results show that the HFB–BAF combined technology is suitable for the treatment of low‐concentration municipal sewage in south China. Copyright © 2005 Society of Chemical Industry     

Phosphorus Removal from Continuous Phosphate-Contaminated Water by Electrocoagulation using Aluminum and Iron Plates Alternately as Electrodes

The objective of this study was to investigate the effects of the main parameters on phosphate removal from continuous phosphate-contaminated water by electrocoagulation based on removal rate and system energy consumption. In the experiment, aluminum and iron plates were used as alternate electrodes and experiment parameters included initial phosphate concentration, current density, flow rate, and initial pH. The results indicated that increases of initial phosphate concentration and flow rate had reduced removal rate and energy consumption. Removal rate and system energy consumption increased by increasing current density. The maximum removal efficiency of 90% was obtained at flow rate 40 mL/min. The minimum energy consumption was 0.165 kWh/m³ at flow rate 100 mL/min. With the increase of initial pH from 4 to 8, the removal rate increased and energy consumption decreased. When the pH was above 8, the removal rate decreased and energy consumption increased. The maximum removal efficiency of 92% and minimum energy consumption of 0.191 kWh/m³ were obtained at pH 8.     

Electrochemical behaviour of titanium in H2SO4-MnSO4 electrolytes

The corrosion of titanium in H₂SO₄ electrolytes (0.001-1.0 M) at temperatures from ambient to 98 °C has been investigated using steady-state polarization measurements. Four distinct regions of behaviour were identified, namely active corrosion, the active-passive transition, passive region and the dielectric breakdown region. The active corrosion and active-passive transition were characterized by anodic peak current (i_m) and voltage (E_m), which in turn were found to vary with the experimental conditions, i.e., d(log?(im))/dpH=−0.8±0.1 and dE_m/dpH which was −71 mV at 98 °C, −58 mV at 80 °C and −28 mV at 60 °C. The activation energy for titanium corrosion, determined from temperature studies, was found to be 67.7 kJ mol⁻¹ in 0.1 M H₂SO₄ and 56.7 kJ mol⁻¹ in 1.0 M H₂SO₄. The dielectric breakdown voltage (E_d) of the passive TiO₂ film was found to vary depending on how much TiO₂ was present. The inclusion of Mn²⁺ into the H₂SO₄ electrolyte, as is done during the commercial electrodeposition of manganese dioxide, resulted in a decrease in titanium corrosion current, possibly due to Mn²⁺ adsorption limiting electrolyte access to the substrate.     

A comparison of the electrochemical recovery of palladium using a parallel flat plate flow-by reactor and a rotating cylinder electrode reactor

The production of catalytic converters generates large amounts of waste water containing Pd²⁺, Rh³⁺ and Nd³⁺ ions. The electrochemical treatment of these solutions offers an economic and effective alternative to recover the precious metals in comparison with other traditional metal recovery technologies. The separation of palladium from this mixture of metal ions by catalytic deposition was carried out using a rotating cylinder electrode reactor (RCER) and a parallel plate reactor (FM01-LC) with the same cathode area (64 cm²) and electrolyte volume (300 cm³). The study was carried out at mean linear flow velocities of 1.27 < ν < 11.36 cm s⁻¹ (120 < Re = υd_e/v < 1080) for the FM01-LC reactor and 20 < ν < 140 cm s⁻¹ (7390 < Re = υd/v < 51,700) for the RCER. The morphology of the palladium deposits at the entrance and at the exit of the electrolyte compartment of the FM01-LC reactor showed the effect of the manifold distributors during the electrolysis; the manifolds generate micro turbulences, increasing the mass transport coefficient in these areas and favouring rapid recovery of palladium ions. More uniform high purity palladium deposits were obtained on the surface of the RCER. The cumulative current efficiency to recover 99% of Pd²⁺ ions in the parallel plate electrode reactor was 35% while the recovery of 97% of Pd²⁺ in the RCER was 62%. The volumetric energy consumption during the electrolysis was 0.56 kW h m⁻³ and 2.1 kW h m⁻³ for the RCER and the FM01-LC reactors, respectively. Using a three-dimensional stainless steel electrode in the FM01-LC laboratory reactor, 99% of palladium ions were recovered after 30 min of electrolysis while in the RCER, 120 min were necessary.     

Non-catalyzed cathodic oxygen reduction at graphite granules in microbial fuel cells

Oxygen is the most sustainable electron acceptor currently available for microbial fuel cell (MFC) cathodes. However, its high overpotential for reduction to water limits the current that can be produced. Several materials and catalysts have previously been investigated in order to facilitate oxygen reduction at the cathode surface. This study shows that significant stable currents can be delivered by using a non-catalyzed cathode made of granular graphite. Power outputs up to 21 W m⁻³ (cathode total volume) or 50 W m⁻³ (cathode liquid volume) were attained in a continuous MFC fed with acetate. These values are higher than those obtained in several other studies using catalyzed graphite in various forms. The presence of nanoscale pores on granular graphite provides a high surface area for oxygen reduction. The current generated with this cathode can sustain an anodic volume specific COD removal rate of 1.46 kg_COD m⁻³ d⁻¹, which is higher than that of a conventional aerobic process. This study demonstrates that microbial fuel cells can be operated efficiently using high surface graphite as cathode material. This implies that research on microbial fuel cell cathodes should not only focus on catalysts, but also on high surface area materials.     

Effect of temperature on the performance of microbial fuel cells

Single and double chamber microbial fuel cells (MFCs) were tested in batch mode at different temperatures ranging from 4 to 35 °C; results were analysed in terms of efficiency in soluble organic matter removal and capability of energy generation. Brewery wastewater diluted in domestic wastewater (initial soluble chemical oxygen demand of 1200 and 492 mg L⁻¹ of volatile suspended solids) was the source of carbon and inoculum for the experiments. Control reactors (sealed container with support for biofilm formation) as well as baseline reactors (sealed container with no support) were run in parallel to the MFCs at each temperature to assess the differences between water treatment including electrochemical processes and conventional anaerobic digestion (in the presence of a biofilm, or by planktonic cells). MFCs showed improvements regarding rate and extent of COD removal in comparison to control and baseline reactors at low temperatures (4, 8 and 15 °C), whilst differences became negligible at higher temperatures (20, 25, 30 and 35 °C). Temperature was a crucial factor in the yield of MFCs both, for COD removal and electricity production, with results that ranged from 58% final COD removal and maximum power of 15.1 mW m⁻³ reactor (8.1 mW m⁻² cathode) during polarization at 4 °C, to 94% final COD removal and maximum power of 174.0 mW m⁻³ reactor (92.8 mW m⁻² cathode) at 35 °C for single chamber MFCs with carbon cloth-based cathodes. Bioelectrochemical processes in these MFCs were found to have a temperature coefficient, Q10 of 1.6.A membrane-based cathode configuration was tested and gave promising results at 4 °C, where a maximum power output of 294.6 mW m⁻³ reactor (98.1 mW m⁻² cathode) was obtained during polarization and a maximum Coulombic efficiency (Y_Q) of 25% was achieved. This exceeded the performance at 35 °C with cloth-based cathodes (174.0 mW m⁻³; Y_Q 1.76%).