Simultaneous dairy wastewater treatment and bioelectricity production in a new microbial fuel cell using photosynthetic Synechococcus

Photosynthetic microbial fuel cell (PMFC) is a novel technology, which employs organic pollutants and organisms to produce electrons and biomass and capture CO2 by bio-reactions. In this study, a new PMFC was developed based on Synechococcus sp. as a biocathode, and dairy wastewater was used in the anode chamber. Different experiments including batch feed mode, semi-continuous feed mode, Synechococcus feedstock to the anode chamber, Synechococcus-Chlorella mixed system, the feedstock of treated wastewater to the cathode chamber, and use of extra nutrients in the anodic chamber were performed to investigate the behavior of the PMFC system. The results indicated that the PMFC with a semi-continuous feed mode is more effective than a batch mode for electricity generation and pollutant removal. Herein, maximum power density, chemical oxygen demand removal, and Coulombic efficiency were 6.95 mW/m2 (450 Ω internal resistance), 62.94, and 43.16%, respectively, through mixing Synechococcus sp. and Chlorella algae in the batch-fed mode. The maximum nitrate and orthophosphate removal rates were 98.83 and 68.5%, respectively, wherein treated wastewater in the anode was added to the cathode. No significant difference in Synechococcus growth rate was found between the cathodic chamber of PMFC and the control cultivation cell. The heating value of the biocathode biomass at maximum Synechococcus growth rate (adding glucose into the anode chamber) was 0.2235 MJ/Kg, indicating the cell's high ability for carbon dioxide recovery. This study investigated not only simultaneous bioelectricity production and dairy wastewater in a new PMFC using Synechococcus sp. but also studied several operational parameters and presented useful information about their effect on PMFC performance.

Hybrid electrocoagulation reactor for dairy wastewater treatment and methodology for sludge reusability for the development of vermicompost

The dairy industry is a high-water-consuming sector, making water conservation crucial, especially in countries like India that are top milk producers and have large populations. This research evaluates the performance and effluent characterization of dairy effluent treatment systems in Kerala using modern, cost-effective technology to address this issue. A hybrid electrocoagulation reactor (HECR) is designed to operate simultaneously in coagulation, and the electrocoagulation process is proposed in this study. The wastewater treatment parameters of the HECR with those of six existing dairy effluent treatment plants using geological mapping and geographic information system (GIS) were studied. According to inverse distance weighted (IDW) interpolation findings, HECR's effluent treatment profile is comparable to existing technologies, with a minimum required retention time of 9.58 h. The results show the HECR treatment efficiency, removing up to 75.15% of turbidity and 94.5% of COD. Moreover, the sludge generated from HECR is transformed into nutrient-rich vermicompost by adding suitable fillers in the ratio of 5:1:3:1 (industrial dairy sludge/HECR sludge: cow dung, dry leaf, and seed vermicompost). The optimal conversion times for vermicompost developed from dairy industrial sludge are 40 days, with nitrogen, phosphorus, and potassium (NPK) values per gram vermicompost of 8.86%, 3.18%, and 3.6%, respectively. For HECR sludge, on the 60th day, the observed NPK value for the developed vermicompost is at 4.76%, 1.46%, and 5.1%. Overall, this research offers a promising solution to treat dairy wastewater and transform generated waste sludge into a valuable resource, highlighting the importance of technology adaptation in the dairy industry.

A critical review of state-of-the-art electrocoagulation technique applied to COD-rich industrial wastewaters

Electrocoagulation (EC) is one of the emerging technologies in groundwater and wastewater treatment as it combines the benefits of coagulation, sedimentation, flotation, and electrochemical oxidation processes. Extensive research efforts implementing EC technology have been executed over the last decade to treat chemical oxygen demand (COD)-rich industrial wastewaters with the aim to protect freshwater streams (e.g., rivers, lakes) from pollution. A comprehensive review of the available recent literature utilizing EC to treat wastewater with high COD levels is presented. In addition, recommendations are provided for future studies to improve the EC technology and broaden its range of application. This review paper introduces some technologies which are often adopted for industrial wastewater treatment. Then, the EC process is compared with those techniques as a treatment for COD-rich wastewater. The EC process is considered as the most privileged technology by different research groups owing to its ability to deal with abundant volumes of wastewater. After, the application of EC as a single and combined treatment for COD-rich wastewaters is thoroughly reviewed. Finally, this review attempts to highlight the potentials and limitations of EC. Related to the EC process in batch operation mode, the best operational conditions are found at 10 V and 60 min of voltage and reaction time, respectively. These last values guarantee high COD removal efficiencies of > 90%. This review also concludes that considerably large operation costs of the EC process appears to be the serious drawback and renders it as an unfeasible approach for handling of COD rich wastewaters. In the end, this review has attempted to highlights the potential and limitation of EC and suggests that vast notably research in the field of continuous flow EC system is essential to introduce this technology as a convincing wastewater technology.

Industrial wastewater treatment using magnesium electrocoagulation in batch and continuous mode

In the present study, the electrocoagulation (EC) performance of a Mg-Mg system was applied for the industrial wastewater treatment, from an industrial park that covers different activities such as: food, automotive, pharmaceutical, chemistry and cosmetics, after primary clarification. The effects of major operating parameters such as pH, reaction time, and current density were investigated for chemical oxygen demand (COD), color, and turbidity removal efficiency. The batch system was found convenient, achieving 63.52% COD, 96% color, and 99.32% turbidity removal at optimized operating conditions of pH 7.12, reaction time of 75 min, and current density of 201.5 A/m². On the other hand, for continuous EC, the process removed approximately 46.58%, 95.96%, and 87.19% of the COD, color, and turbidity respectively, at 90 min of retention time, current density 440 A/m², and a rate of 20 mL/min. Additionally, concerning nutrient removal (N and P), the EC system with Mg electrodes was highly efficient; batch treatment removed 97% of total phosphorus and 67% of ammoniacal nitrogen, whereas the continuous treatment removed 98.5% of total phosphorus and 83% of ammoniacal nitrogen. The sludge characterization before and after EC treatment was made by SEM, EDS, Fluorescence spectroscopy, IR spectroscopy. Minerals such as chlorite, crossite, richterite, pyroaurite, langbeinite as weel as aliphatic and polysubstituted aromatics compounds, sulfates and phosphates inorganic ions, and organic phosphorus were reduced. The energy cost in the batch EC is US$0.05/m³. A numerical CFD model was used to estimate the velocity fields and guarantee the presence of turbulent kinetic energy within a continuous flow reactor.

Removal of color and turbidity in sugarcane juice treated by electrocoagulation with aluminum electrodes

Abstract The liming (Ca(OH)2 addition) and sulfitation (HSO3- addition) is the conventional treatment for purification of sugarcane juice (SCJ) in sugar cane mills to crystal sugar production. Although, the sulfite has been associated to human health problems, this industrial step kept untouchable or few studies have been made to change this scenery. This work aimed to evaluate the variables which influence the electrocoagulation performance on the SCJ purification as a sulfur-free crystal sugar process. A fractional factorial design with the surface response methodology was used to evaluate the influence of voltage, pH, soluble solids total (Brix), temperature and distance between the electrodes in the electrocoagulation process. The outputs were turbidity, juice color, sucrose contents (as pol%juice) and Reducing Sugars (RS). Residual aluminum was analyzed by voltammetry to control de aluminum releasing into the treated juice. The electrocoagulation reduced color and turbidity, in special at low pH (2.5), highest voltage (25 V) and minimal distance of electrode (1.0 cm). Although in this conditions, sucrose was converted into RS indicating partial hydrolysis. In this work, the most part of residual aluminum went to floated and precipitated phases (76.8% and 18.1%, respectively), whereas only 5.1% remained in the SCJ clarified. Electrocoagulation/electroflotation proved to be a potential technique as a substitute for sulfitation in SJC treatment, which ensures the production of safe food for humans.

Removal of Heavy Metals from Wastewaters: A Challenge from Current Treatment Methods to Nanotechnology Applications

Removing heavy metals from wastewaters is a challenging process that requires constant attention and monitoring, as heavy metals are major wastewater pollutants that are not biodegradable and thus accumulate in the ecosystem. In addition, the persistent nature, toxicity and accumulation of heavy metal ions in the human body have become the driving force for searching new and more efficient water treatment technologies to reduce the concentration of heavy metal in waters. Because the conventional techniques will not be able to keep up with the growing demand for lower heavy metals levels in drinking water and wastewaters, it is becoming increasingly challenging to implement technologically advanced alternative water treatments. Nanotechnology offers a number of advantages compared to other methods. Nanomaterials are more efficient in terms of cost and volume, and many process mechanisms are better and faster at nanoscale. Although nanomaterials have already proved themselves in water technology, there are specific challenges related to their stability, toxicity and recovery, which led to innovations to counteract them. Taking into account the multidisciplinary research of water treatment for the removal of heavy metals, the present review provides an updated report on the main technologies and materials used for the removal of heavy metals with an emphasis on nanoscale materials and processes involved in the heavy metals removal and detection.

Copper (II) removal in a column reactor using electrocoagulation: Parametric optimization by response surface methodology using central composite design

In the present work, electrocoagulation was applied for copper removal from aqueous solution employing iron electrodes in a cylindrical reactor. A four-factorial central composite design (CCD) based on response surface methodology (RSM) was applied to study the effect of various process parameters on removal efficiency and energy consumption as the responses. On optimization, maximum removal efficiency up to 95% was attained with energy consumption as 0.903 W-hour per gram removal of Cu (II) at applied current 0.26 A, initial copper concentration of 27.8 ppm, application time of 5.4 min and pH 7. The interaction between the process variables was evaluated by using the obtained 3-D plots. The models generated were validated by analysis of variance (ANOVA). Studies carried on Cu (II) removal rate showed adsorption suited pseudo-Ist order kinetics best. Overall, the electrocoagulation process proved efficient, low cost and a promising alternative to conventional treatment procedures in removing Cu (II). PRACTITIONER POINTS: Adsorption over hydroxide/polyhydroxide complexes of Fe assisted in enhanced removal of Cu (II) by EC. Higher concentrations treated at lower current but longer duration reduces energy. pH was found to be the deterministic factor for coagulation. CCD-based optimization reduced energy consumption substantially.

Evaluation of Electrochemical Methods for Poultry Slaughterhouse Wastewater Treatment

Understanding the efficiency of different wastewater treatment technologies tested under real conditions is essential for successful decision making by engineers and managers. In this study, real poultry slaughterhouse wastewater coming from defeathering, cooling, and evisceration processes was treated using a lab-scale electrochemical process by use of iron-iron (Fe-Fe), iron-graphite (Fe-Gr) and aluminum-graphite (Al-Gr) electrode combinations. A water quality index (WQI) was developed and used as a tool for evaluating and classifying the effectiveness of different electrode combinations. The Al-Gr electrode combination showed an impressive performance achieving an “excellent” status for all of the three studied sources of wastewater with a WQI ranging from 13 to 34. The Fe-Gr electrode combination showed an “excellent” status performance for the wastewater from the cooling process as classified by the WQI and “good water” class for the defeathering and evisceration processes. The lower performance, which was highly affected by the increase in turbidity, was observed for the Fe-Fe electrode combination with a “poor water” status for the wastewater coming from defeathering and cooling processes and “good water” status for evisceration process.

Electrocoagulation: A Promising Method to Treat and Reuse Mineral Processing Wastewater with High COD

Mineral processing wastewater contains large amounts of reagents which can lead to severe environmental problems, such as high chemical oxygen demand (COD). Inspired by the wastewater treatment in such industries as those of textiles, food, and petrochemistry, in the present work, electrocoagulation (EC) is applied for the first time to explore its feasibility in the treatment of wastewater with an initial COD of 424.29 mg/L from a Pb/Zn sulfide mineral flotation plant and its effect on water reuse. Typical parameters, such as anode materials, current density, initial pH, and additives, were characterized to evaluate the performance of the EC method. The results showed that, under optimal conditions, i.e., iron anode, pH 7.1, electrolysis time 70 min, 19.23 mA/cm2 current density, and 4.1 g/L activated carbon, the initial COD can be reduced to 72.9 mg/L, corresponding to a removal rate of 82.8%. In addition, compared with the untreated wastewater, EC-treated wastewater was found to benefit the recovery of galena and sphalerite, with galena recovery increasing from 25.01% to 36.06% and sphalerite recovery increasing from 59.99% to 65.33%. This study confirmed that EC is a promising method for the treatment and reuse of high-COD-containing wastewater in the mining industry, and it possesses great potential for wide industrial applications.

Suitability of aluminum material on sugar industry wastewater with chemical and electrochemical treatment processes

Aluminum is a valuable material, which can be used for water and wastewater treatment. It exists in metal as well as in salt form. The efficiency of water and wastewater treatment depends upon the technology applied to treat. Sugarcane industry is coming under those industries which have a large amount of freshwater and release large amount of effluent. The goal of this research work is to study the behavior of aluminum metal and salt for the treatment of sugar industry wastewater on chemical oxidation and electrochemical oxidation. The effect of pH, dosing, temperature and catalysis on metal and salt has been also studied with both treatment methods. The results show that maximum 90% of chemical oxygen demand and 94% of color removal can be achieved with an aluminum electrode (electrocoagulation) at optimum conditions, pH 7, current density 178 A/m2, electrode distance 20 mm, and salt solution 0.5 M NaCl. In the same way, 81% chemical oxygen demand and 85% color removal were achieved with alum for the 0.5 M lime solution, at 50 mM mass loading, 21 °C operating temperature and optimum pH of 7, respectively. The sludge generated after treatment was also analyzed with settling filtration, thermal, FTIR and SEM.

Efficient Removal of Hexavalent Chromium from Wastewater with Electro-Reduction

Removal of hexavalent chromium had attracted much attention as it is a hazardous contaminant. An electrocoagulation-like technology electro-reduction was applied. The chromium (VI) in the wastewater was reduced to chromium (III) by the electron supplied by electricity power and Fe2+, formed from corrosion of steel electrodes in acidic conditions. The mechanism and parameters affecting the reaction were investigated. The results optimized by response surface methodology indicated that the influence of single factor on the reduction efficiency followed the order: A: dosage of H2SO4 > C: reaction time > D: reaction temperature > B: current intensity. The reduction efficiency was hardly affected by current intensity, while it was increased with the increasing of reaction time and acid concentration. The reducing agent, Fe2+ an and extra free electron, acted as a reducing agent and could easily reduce hexavalent chromium to trivalent chromium at high temperatures in an acidic medium.

Treatment of paper-recycling wastewater by electrocoagulation using aluminum and iron electrodes

Treatment of industrial wastewater by electrocoagulation (EC) is one of the most efficient methods to remove pollutants. Paper-recycling wastewater is a complex mixture containing toxic and recalcitrant substances, indicating complexity and difficulty of its treatment. The aim of the present study was to assess the effectiveness of paper-recycling wastewater treatment by EC process using aluminum (Al) and iron (Fe) plate electrodes. Removal of chemical oxygen demand (COD), total suspended solids (TSS), color and ammonia from paper-recycling mill effluent was evaluated at various electrolysis times (10-60 min), voltage (4-13 V) and pH (3.5-11). The optimum process conditions for the maximum removal of COD, TSS, color and ammonia from paper-recycling industry wastewater have been found to be pH value of 7, treatment time of 60 min and voltage of 10 V. Under optimum operating conditions, the removal capacities of COD, TSS, color and ammonia were 79.5%, 83.4%, 98.5% and 85.3%, respectively. It can be concluded that EC could be considered as an effective alternative for treatment of paper-recycling wastewater.