Effect of recirculation of currant-finishing wastewater (CFW) on its composition.

The feasibility of recirculation of currant-finishing wastewater in a currant-wash process was investigated in a laboratory scale plant. Recycle ratios from 0% to 95% were examined. By increasing the recycle ratio, effluent BOD increased from 681 to 5378 mg/l, effluent COD from 3808 to 43,722 mg/l, total suspended solids from 12.3 to 57.7 g/l, total sugars from 2.57 to 42.13 g/l, total phosphorus from 0.79 to 5.14 mg/l, total Kjeldahl nitrogen from 7.36 to 51.9 mg/l and total phenolic compounds from 0.095 to 1.13 g/l, while fresh water addition decreased from 6 to 0.3 kg/kg of currants processed and total sugars loss from 15.43 to 12.64 g/kg of currants processed. For a recycle ratio of 95%, the mass of currants recovered as a final product increased by 10% due to the proportional decrease in the sugars wasted per kg of currants processed.

RETRACTED: Assessment of compost from vinasse and olive stone residue.

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Thermal-alkaline solubilization of waste activated sludge as a pre-treatment stage for anaerobic digestion.

This work studied the hydrolysis kinetics and the solubilization of waste activated sludge under a medium range temperature (50-90 degrees C) and pH in the alkaline region (8-11), as a pretreatment stage for anaerobic digestion. The hydrolysis rate for the solubilization of volatile suspended solids (VSS) followed a first-order rate. A linear polynomial hydrolysis model was derived from the experimental results leading to a satisfactory correlation between the hydrolysis rate coefficient, pH, and temperature. At pH 11 and a temperature of 90 degrees C the concentration of the VSS was 6.82%, the VSS reduction reached 45% within ten hours and at the same time the soluble COD was 70.000 mg/l and the total efficiency for methane production 0.28 l of CH4 per g of VSS loading.

Small sewage treatment works using a Fenton oxidation method.

This paper describes an oxidation treatment of Domestic Wastewater (DW) using Fenton's reagent (H2O2/Fe2+). In this technique, DW was mixed with ferrous sulfate (523 mg l(-1)) and hydrogen peroxide (300, 600 and 900 mg l(-1) respectively). Due to the strong oxidizing potential of the hydroxyl radicals and other oxidants the organic pollutants and nutrients (organic nitrogen, phosphorous) were wet oxidized to carbon dioxide, and nitrogen oxides and phosphorous was precipitated as Fe3(PO4)2. Experiments were run in a batch, laboratory-scale, pilot-plant, at 30 degrees C and the efficiency of oxidation was studied in relation to oxidation time. According to the experimental results a 82% COD reduction, a 80% BOD5 reduction, a 100% fats and oils reduction, a 95% Total Kjeldahl Nitrogen (TKN) reduction, a 96% Total Suspended Solids (TSS) reduction and a 93% total phosphorous reduction were achieved. It is concluded that the application of chemical oxidation of DW is more advantageous compared to conventional biological treatment especially for small works.

Electrochemical treatment in relation to pH of domestic wastewater using Ti/Pt electrodes.

This paper describes an electrochemical treatment of domestic wastewater (DW) using 0.8% (w/v) sodium chloride as electrolyte. In this technique, DW was passed through an electrolytic cell using Ti/Pt as anode and Stainless Steel 304 as cathode. Due to the strong oxidizing potential of the chemicals produced (chlorine, oxygen, hydroxyl radicals and other oxidants), the organic pollutants and nutrients (organic nitrogen, phosphorous) were wet oxidized to carbon dioxide, and nitrogen as well as phosphorous was precipitated as Ca(3)(PO(4))(2). Experiments were run in a continuous, laboratory-scale, pilot plant, at 40 degrees C and the efficiency of oxidation was studied in relation to pH. It was found that in alkaline conditions the electrolysis was more efficient. At pH 9, NaCl concentration 0.8% (w/v), current density 0.075 A/cm(2) and for 1h of electrolysis, COD was reduced by 89%, volatile suspended solids (VSS) by 90%, ammonia nitrogen by 82% and total phosphorous by 98%. The efficiency of electrolysis went up to 35 g COD(r)/(hm(2)A) and the energy consumption to 12.4 kWh/kg COD(r). It is concluded that the application of electrolytic oxidation of DW is more advantageous compared to conventional biological treatment especially for small works.

Impact of thermal treatment on metal in sewage sludge from the Psittalias wastewater treatment plant, Athens, Greece.

This paper describes a laboratory study that examined the effect of thermal treatment at four different temperatures on the behavior of heavy metals in the anaerobically treated primary sludge from the Psittalias wastewater treatment plant. The sewage sludge was found to contain significant amounts of heavy metals (Cr, Cu, Fe, Ni, Pb and Zn). The metal form distribution in the sludge samples which was determining by the application of a sequential extraction procedure revealed that a significant portion of metals was embodied in the organic and reducible fractions. Treatment at 105, 250, 650 and 900 degrees C demonstrated significant conversions of the metals to a less mobile form as well as removal by vaporization. By applying sequential analysis, it was found that most of the metals were removed from the initial mobile phases to more stable ones. Also, significant amounts were transformed to the gaseous phase.

Electrochemical oxidation of a textile dye wastewater using a Pt/Ti electrode.

Textile dye wastewater (TDW) from a reactive azo dyeing process was treated by an electrochemical oxidation method using Ti/Pt as anode and stainless steel 304 as cathode. Due to the strong oxidizing potential of the chemicals produced (chlorine, oxygen, hydroxyl radicals and other oxidants) when the wastewater was passed through the electrolytic cell the organic pollutants were oxidized to carbon dioxide and water. A number of experiments were run in a batch, laboratory-scale, pilot-plant, and the results are reported here according to residence time and initial addition of HCl in raw wastewater. When of 2 ml of HCl 36% were added and after 18 min of electrolysis at 0.89 A/cm(2), chemical oxygen demand (COD) was reduced by 86%, biochemical oxygen demand (BOD(5)) was reduced by 71%, ADMI color units were reduced by 100%, and TKN was reduced by 35%. The biodegradability of the wastewater was improved because the COD/BOD ratio decreased from 2.16 to 1.52. At the same time the efficiency of the electrode was about 170 g h(-1) A(-1) m(-2). and the mean energy consumption was 21 kW h/kg of COD. These results indicate that this electrolytic method could be used for effective TDW oxidation or as a feasible detoxification and color removal pretreatment stage for biological post treatment.