Effectiveness of potassium ferrate (VI) as a green agent in the treatment and disinfection of carwash wastewater

Contribution identification of hydrolyzed products of potassium ferrate on promoting short-chain fatty acids production from waste activated sludge

Potassium ferrate (K2FeO4) has been extensively employed to promote short-chain fatty acids (SCFAs) production from anaerobic fermentation of waste activated sludge (WAS) because of its potent oxidizing property and formation of alkaline hydrolyzed products (potassium hydroxide, KOH and ferric hydroxide, Fe(OH)3). However, whether K2FeO4 actually works as dual functions of both an oxidizing agent and an alkalinity enhancer during the anaerobic fermentation process remains uncertain. This study aims to identify the contributions of hydrolyzed products of K2FeO4 on SCFAs production. The results showed that K2FeO4 did not execute dual functions of oxidization and alkalinity in promoting SCFAs production. The accumulation of SCFAs using K2FeO4 treatment (183 mg COD/g volatile suspended solids, VSS) was less than that using either KOH (192 mg COD/g VSS) or KOH & Fe(OH)3 (210 mg COD/g VSS). The mechanism analysis indicated that the synergistic effects caused by oxidization and alkalinity properties of K2FeO4 did not happen on solubilization, hydrolysis, and acidogenesis stages, and the inhibition effect caused by K2FeO4 on methanogenesis stage at the initial phase was more severe than that of its hydrolyzed products. It was also noted that the inhibition effects of K2FeO4 and its hydrolyzed products on the methanogenesis stage could be relieved during a longer sludge retention time, and the final methane yields using KOH or KOH & Fe(OH)3 treatment were higher than that using K2FeO4, further confirming that dual functions of K2FeO4 were not obtained. Therefore, K2FeO4 may not be an alternative strategy for enhancing the production of SCFAs from WAS compared to its alkaline hydrolyzed products. Regarding the strong oxidization property of K2FeO4, more attention could be turned to the fates of refractory organics in the anaerobic fermentation of WAS.

Removal of phosphate from brewery wastewater by cerium(III) chloride originating from spent polishing agent: Recovery and optimization studies

This paper presents the possibility of using hydrated cerium(III) chloride (CeCl₃∙7H₂O) recovered from a spent polishing agent containing cerium(IV) dioxide (CeO₂) to remove phosphate and other impurities from brewery wastewater (phosphate 43.0 mg/L, total P 19.8 mg/L, pH 7.5, COD_(Cr) 827 mg O₂/L, TSS 630 mg/L, TOC 130 mg/L, total N 46 mg/L, turbidity 390 NTU, colour 170 mg Pt/L. CCD (Central Composite Design) and RSM (Response Surface Methodology) were applied to optimise the brewery wastewater treatment process. The removal efficiency (mainly of PO₄^3-) was the highest under optimal conditions (pH 7.0-8.5, Ce³⁺:PO₄^3- molar ratio of 1.5-2.0). Applying recovered CeCl₃ under optimal conditions yielded a treated effluent in which the concentration of PO₄^3- decreased by 99.86 %, total P by 99.56 %, COD_(Cr) by 81.86 %, TSS by 96.67 %, TOC by 60.38 %, total N by 19.24 %, turbidity by 98.18 %, and colour by 70.59 %. The Ce³⁺ ion concentration in the treated effluent was 0.058 mg/L. These findings suggest that CeCl₃‧7H₂O recovered from the spent polishing agent may constitute an optional reagent for phosphate removal from brewery wastewater. The sludge from wastewater treatment can be recycled for Ce and P recovery. The recovered cerium can be reused for wastewater treatment, creating a cyclic cerium cycle in the process, and the recovered phosphorus can be used, for example, for fertilization purposes. The optimised cerium recovery and application is in accordance with the ideas of circular economy.

The Application of Polyethersulfone Ultrafiltration Membranes for Separation of Car Wash Wastewaters: Experiments and Modelling

The wastewater generated as a result of car washes is considered a new source of water. However, recovered water must meet the required quality criteria for reuse. For this purpose, the ultrafiltration (UF) process can be successfully used. The main aim of the present work was to investigate the influence of the membrane's molecular weight cut-off (MWCO) on the UF performance in terms of the fouling phenomenon and retention degree of car wash wastewater. Moreover, for a better understanding of the fouling mechanisms, Hermia's model was used. The experimental studies were conducted with the use of two polyethersulfone (PES) membranes (MWCO of 10 kDa and 100 kDa). It has been noted that the used membranes provided a high-quality permeate and excellent turbidity removal, up to 99%. Moreover, it has been noted that the MWCO membrane has a significant impact on the fouling mechanism. Generally, a much greater intensity of fouling for the membrane with MWCO of 100 kDa was observed. Results obtained in the present study showed that both real wastewaters and the clean solutions used for washing cars cause the fouling phenomenon. It has been proven that rinsing the membranes with water is not sufficient to recover the initial membrane's performance. Hence, periodic chemical cleaning of the membranes was required. Fitting the experimental data to Hermia's model allowed us to indicate that membranes with MWCO of 100 kDa are more prone to intermediate blocking. To sum up, the findings suggest that for the UF of the car wash wastewater, the use of membranes with MWCO equal to 10 kDa is recommended.

Carbonate and bicarbonate ions impacts on the reactivity of ferrate(VI) for 3,4-dichlorophenol removal

Carbonate and bicarbonate ions are common constituents found in wastewater and natural water matrices, and their impacts on the reactivity of ferrate(VI) (Fe(VI)) with 3,4-dichlorophenol (3,4-DCP) were investigated by determining second-order rate constants of 3,4-DCP removal by Fe(VI) in the presence of CO₃^2- and/or HCO₃^-. The second-order rate constants decreased from 41.75 to 7.04 M^-1 s^-1 with an increase of [CO₃^2-] from 0 to 2.0 mM, indicating that CO₃^2- exhibits an inhibitory effect on 3,4-DCP removal kinetics, and experiments on pH effect, radical quenching, and Fe(VI) stability were conducted to explore possible reasons for its effect. Under identical pH conditions, the rate constant in NaOH medium was always higher than in Na₂CO₃ medium, suggesting that the inhibitory effect partially comes from an increase in alkalinity. Furthermore, the scavenging of hydroxyl radical by carbonate ion also contributed to the inhibitory effect of CO₃^2-. On the other hand, the enhancement effect of CO₃^2- depending on the increase in Fe(VI) stability was found, but did not exceed its inhibitory effect. In addition, 3,4-DCP removal kinetics was not affected by HCO₃^-, while synergistically inhibited by CO₃^2-/HCO₃^-. Moreover, 3,4-DCP removal efficiency was substantially suppressed in the presence of CO₃^2-, while the slight enhancement effect of HCO₃^- and the synergistic inhibitory effect of CO₃^2-/HCO₃^- were observed. The experimental results clearly demonstrated that carbonate and bicarbonate ions play an important role in the process of 3,4-DCP removal by Fe(VI) and should not be considered only as scavengers.

Combined coagulation and membrane treatment for anaerobically digested manure centrate: Contaminant residuals and membrane fouling

To realize water and resource recovery from anaerobically digested manure centrate, the effect of combined coagulation and membrane treatment on contaminant residuals and membrane fouling was investigated. Two combined treatments were used to explore the properties of the retention of nutrients and the removal of risk pollutants. Behaviors and reversibility of membrane fouling after combined treatment were also examined. The result showed that the combined treatment significantly improved the water recovery rate by more than 60% and achieved better nutrient enrichment. Meanwhile, the combined treatment had certain removal effects on heavy metals and antibiotics, which promoted the safety of farmland utilization of anaerobically digested manure centrate. Moreover, the combined treatment reduced the membrane fouling by removing most suspended solids in the digested centrate. Combined coagulation and membrane treatment show great potential for practical applications in the treatment of anaerobically digested manure centrate due to the easy operation and excellent effect. This work provides a technical reference for the harmless and resource recovery of anaerobically digested manure centrate.

Wastewater substrate disinfection for cyanobacteria cultivation as tertiary treatment

Cultivation of microalgae or/and cyanobacteria in nutrient-rich wastewaters offers an opportunity for enhancing sustainability of tertiary wastewater treatment processes via resources/energy recovery/production, mitigation of emitted GHGs and provision of added value products. However, maintaining a monoculture in wastewater-media constitutes a significant challenge to be addressed. In this regard, the present work assesses the efficiency of the low-cost wastewater substrate disinfection techniques of filtration, use of NaClO, H₂O₂ or Fe(VI), as a preliminary treatment stage upstream a cyanobacteria cultivation photobioreactor. The growth rate of cyanobacterium Synechococcus elongatus PCC 7942, and nitrate and phosphate removal rates, were experimentally assessed in cultivation setups with biologically treated dairy wastewater that had been subjected to a single or a synergetic couple of disinfection techniques. The results showed that filter thickness has a greater effect on disinfection efficiency than filter pore size. Furthermore, the disinfection efficiency of Fe(VI), which was produced on-site by electrosynthesis via a Fe⁰/Fe⁰ cell, was greater than that of NaClO and H₂O₂. Filtration at ≤ 1.2-μm pore size coupled with chemical disinfection led to unhindered Synechococcus elongatus PCC 7942 growth and efficient nitrate and phosphate removal rates, at dosages, in terms of Concentreation-Time (CT) product, of CT ≥ 270 mg min L^-1 for NaClO and CT ≥ 157 mg min L^-1 for Fe(VI). The coagulation action of Fe(III) species that result from Fe(VI) reduction and the oxidation action of Fe(VI) can assist in turbidity, organic compounds and phosphorous removal from wastewater media. Moreover, the residual iron species can assist in Synechococcus elongatus PCC 7942 harvesting and may enhance photosynthesis rate by increasing light transfer efficiency. Thus, a filtration configuration coupled with chemical disinfection, preferably using ferrates, downstream of sedimentation tank of a secondary biological wastewater treatment stage is proposed as a necessary, efficient and low-cost disinfection technique for full-scale scale implementation of cyanobacteria cultivation as tertiary wastewater processes.

Treatment of Tanning Effluent Using Seaweeds and Reduction of Environmental Contamination

One of the main sources of dangerous chemicals that are dumped untreated into land and water bodies and have a negative influence on the ecosystem are industrial effluents. Seaweeds are currently used for treating industrial effluent effectively. The technology is at a maturing stage. This paper reviews the characterization and cultivation of seaweeds for wastewater treatment. In this present study, different extracts of four seaweeds such as Gracilaria edulis, Sargassum wightii, Turbinaria ornata, and Kappaphycus alvarezii, from the Mandapam coastal regions were analyzed. The seaweeds are used to treat the leather industry effluents collected from EKM leather processing company, Erode, Tamil Nadu, India. Among all, extracts of Gracilaria edulis survived at different concentrations of TDS: 15,000, 25000, and 35000 mg/l. Out of these different ranges, TDS of about 25000 mg/l seaweed named Gracilaria edulis reduced more amounts of chemicals present in the effluent like TDS (93.90%), phosphates (72.71%), nitrate (75.08%), nitrite (76.92%), and turbidity (99.01%) content. Additionally, we produce the quality and strength of agar gel from the cultivation of Gracilaria edulis by the Nikansui method. Finally, we got the extraction procedure to obtain a higher yield of about 10.26% and a maximum gel strength of 92.06 g·cm−2 while maintaining the melting point at 78°C.

Valorization of waste chicken skin for conjugated linoleic acid (CLA) production: optimization using response surface methodology

The valorization of waste chicken skin fat (WCSF) for conjugated linoleic acid (CLA) production was performed by photoisomerization and optimized the process conditions for high CLA production by response surface methodology. The fat extraction yield from waste chicken skin was approximately 52%. The linoleic acid content of the fat obtained from waste chicken skin was increased by the fractionation process approximately 2 times, up to 52%. Optimum iodine amount and processing time for predicted maximum total CLA amount were determined as 0.87% and 116.36 h, respectively. The maximum total CLA amount was predicted and produced experimentally as 32.14% and 29.01%, respectively. Additionally, iodine amount, processing time, and their interaction significantly affected the amount and variety of produced CLA isomers. The results indicated that dominant isomers produced by photoisomerization of WCSF were trans, trans isomers. However, the amount of cis 9, trans 11 and trans 10, cis 12 CLA isomers could be more increased by optimizing the production parameters. The present study indicated that waste chicken skin could be valorized in CLA production by photoisomerization and obtained high value-added product, and also a more economical and faster CLA production could be realized.