Recovery of Cerium Salts from Sewage Sludge Resulting from the Coagulation of Brewery Wastewater with Recycled Cerium Coagulant.

Due to the high cost and limited sources of cerium coagulants, it is extremely important to take measures to recycle this raw material. This paper presents the new possibility of recovering cerium(III) chloride, cerium(III) sulphate, cerium(IV) sulphate, and potentially phosphate from sewage sludge (101.5 g/kg Ce and 22.2 g/kg total P) through a brewery wastewater treatment process using recycled CeCl3 as a coagulant. In order to recover the Ce and P, the sludge was subjected to extraction using an HCl solution. Optimal process conditions were determined by means of central composite design and response surface methodology (CCD/RSM) for three input parameters (HCl mass, reaction time, and extractant volume). Under optimal conditions (0.35 g HCl per 1 g of sludge, 40 min reaction time, extractant volume of 25 mL per 1 g of sludge), the highest efficiency obtained was 99.6% and 97.5% for Ce and P, respectively. Cerium(III) oxalate as Ce2(C2O4)3∙10H2O was precipitated from the obtained solution using H2C2O4 (99.97%) and decomposed into CeO2 (at 350 °C), which was afterwards subjected to a reaction with HCl (30%, m/m) and H2O2 (30%, m/m), which led to the crystallisation of CeCl3∙7H2O with a purity of 98.6% and a yield of 97.0%. The obtained CeO2 was also subjected to a reaction with H2SO4 (96%, m/m) and H2O2 (30%, m/m), which produced Ce2(SO4)3 with a yield of 97.4%. The CeO2 was also subjected to a reaction with only H2SO4 (96%, m/m), which produced Ce(SO4)2 with a yield of 98.3%. The filtrate obtained after filtering the Ce2(C2O4)3∙10H2O contained 570 mg/L of P, which enabled its use as a source of phosphorus compounds. The presented processes of Ce and potentially P recovery from sewage sludge originating from brewery wastewater contribute to the idea of a circular economy.

Evaluation of the mobility of heavy metals in the sediments originating from the post-galvanic wastewater treatment processes.

The article presents the assessment of heavy metals mobility in sediments from the process of galvanic wastewater treatment (pH 2.5, Co 1.5 mg/L, Cr6+ < 0.02 mg/L, Cr(total) 62 mg/L, Cu 110 mg/L, Ni 129 mg/L and Pb 59 mg/L) based on the use of hydroxides (Ca(OH)2, NaOH) as well as inorganic and organic sulphur compounds (Na2S, sodium dimethyldithiocarbamate (DMDTC), sodium trithiocarbonate (Na2CS3), trimercapto-s-triazine trisodium salt, TMT). The leachability was assessed after 1, 7, 14 and 21 days of sediment contact with the leaching agent (deionized water). FeCl3 was used as a coagulant. The efficiency of metal removal changed within a range of 99.67-99.94% (for NaOH), 98.80-99.75% (for TMT), 99.67-99.92% (for DMDTC), 99.67-99.91 (for Na2CS3). The heavy metal content in the obtained precipitates changed within the following ranges: 0.1-0.2 g/kg (Co), 9.8-14.7 g/kg (Cr), 23.6-39.8 g/kg (Cu) 30.5-43.2 g/kg (Ni), 24.3-33.1 g/kg (Pb) and 12.2-18.7 g/kg (Cd). The leachability tests revealed the release of 34-37% of Cd, 6.4-7.5% of Ni and 0.06-0.07% of Cu after using an excess of Na2CS3 as the precipitant. The use of NaOH resulted in the release of 0.42-0.46% of Cr from the sediment, and the use of TMT 0.03-0.34% of Ni. The best immobilization of heavy metals was observed in the case of the precipitate resulting from the use of DMDTC as a precipitating agent. The findings may be useful for predicting the mobility of heavy metals in the sludge and assessing the risk involved so as to support their removal and management.

Evaluation of the stability of heavy metal-containing sediments obtained in the wastewater treatment processes with the use of various precipitating agents.

The article presents the results of research on the leachability of selected heavy metals (cadmium, nickel, chromium, cobalt, lead, and copper) from solid waste obtained in laboratory processes involved in the industrial treatment of wastewater generated in metal surface treatment plants. The test sludges were precipitated using sodium hydroxide solution, calcium hydroxide suspension, 45% solution sodium trithiocarbonate (Na2CS3), 15% solution trimercapto-s-triazine, sodium salt (TMT), and 40% solution sodium dimethyldithiocarbamate (DMDTC). The precipitates were treated with artificial acid rain and artificial salt water. After 1, 7, 14, and 21 days of leaching, the concentration of Cd, Co, Cr, Cu, Pb, and Ni in the leachate was determined. Artificial acid rain leached Ni and Cd to a maximum concentration of 724 mg/L and 1821 mg/L, respectively, from the sludge obtained after the application of Na2CS3, while artificial salt water leached Ni in the maximum amount of 466 mg/L and Cd-max. 1320 mg/L. When Ca(OH)2/NaOH was used, the leaching of Cr reached a similar level for both leaching agents, i.e., the maximum for artificial acid rain was 72.2 mg/L and the maximum for artificial salt water 71.8 mg/L. The use of Na2CS3 or Ca(OH)2/NaOH poses a risk of some heavy metals entering the environment, which may have a negative impact on living organisms, whereas the sludges obtained with the use of DMDTC and TMT as precipitants were the most stable under the experimental conditions and did not pose a potential environmental hazard.

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 PO43-) was the highest under optimal conditions (pH 7.0-8.5, Ce3+:PO43- molar ratio of 1.5-2.0). Applying recovered CeCl3 under optimal conditions yielded a treated effluent in which the concentration of PO43- 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.