Simultaneous removal of organic and inorganic pollutants in tannery wastewater using electrocoagulation technique

Tannery wastewater can cause severe environmental problems related to its high chemical oxygen demand, high biochemical oxygen demand, high total suspended solids, high oil and grease contents together with the elevated chromium concentration and objectionable color. The one-step electrocoagulation process was carried out to simultaneously remove chromium and various pollutants from tannery wastewater at ambient temperature in the laboratory scale. Low-cost commercial iron plates were employed in this study as anodes and cathode materials. Effects of various parameters were investigated including types of electrode configuration, initial pH of wastewater (7–9), current density (15.7–24.6 Am⁻²) and circulating flow rate of wastewater (0–3.67 lmin⁻¹). The optimum condition was found by applying the mono-polar electrode in a parallel connection at the current density of 22.4 Am⁻², flow rate of wastewater of 3.67 lmin⁻¹ and 20 min electrolysis time. The initial pH of wastewater ranging from 7–9 provided the similar removal efficiency. At optimum condition, more than 95% of chromium and pollutants except TKN and TDS were eliminated from the wastewater and the properties of the treated wastewater met the standard and permitted to discharge into the environment. The required energy consumption at optimum condition was less than 0.13 kWhm⁻³ wastewater. In addition, the COD reduction was fit very well with the first-order kinetics model.     

Electrochemical reforming of an acidic aqueous glycerol solution on Pt electrodes

The feasibility of the electrochemical conversion of glycerol to alternative, more valuable compounds was evaluated with platinum electrode under galvanostatic conditions. The results indicated a potentially good feasibility of reforming glycerol by electrolysis, particularly under strong acidic conditions (pH 1). Indeed, under controlled conditions at pH 1, various commercially valuable compounds, such as propanediol, glycidol, and 2-propenol, amongst others, were produced. The mechanism for the generation of the key compounds is proposed.     

Simultaneous removal of chromium and organic pollutants in tannery wastewater by electroprecipitation technique

The simultaneous removal of chromium and other organic pollutants from tannery wastewater was investigated in a batch electrochemical membrane reactor. This reactor, having a total capacity of 1 liter, was separated into two compartments (anodic and cathodic compartments) by using an anionic membrane. A stainless steel sheet with the square holes having total surface area of 0.0215 m² and a Ti/RuO₂ grid was used as the cathode and anode, respectively. The results indicated that the optimum condition for removal of chromium from tannery wastewater was found at the current density of 60.5 A/m² at initial pH of 4.5. At this condition, more than 98% of chromium was removed within 60 min. Some organic pollutants contained in wastewater such as oil and grease, color and the level of biochemical oxygen demand (BOD), chemical oxygen demand (COD) and total kjeldahl nitrogen (TKN) were also markedly reduced.     

Purification of crude glycerol derived from waste used-oil methyl ester plant

The purification of crude glycerol from a biodiesel plant using waste used-oil as a raw material was carried out on a laboratory scale by using the combined chemical and physical treatments based upon repeated cycles of acidification to the desired pH within the range of 1–6 using 1.19 M H₂SO₄, allowing phase separation and harvesting of the glycerol-rich middle phase followed by neutralization of the harvested glycerol phase with 12.5M NaOH. Subsequently, the glycerol-enriched fraction was extracted by ethanol. The results indicated that increasing the pH of the acidification step led to an increased yield of the glycerol-rich layer and decreased amount of inorganic salt and free fatty acids phase. Under strong acid conditions, large quantities of fatty acid and salt in the glycerol-enriched fraction were eliminated and, at pH 1, high purity glycerol (∼93.34%) with relatively low contaminant levels (0.00045% (w/w) ash and 5.16% (w/w) MONG) was obtained.