Treatment Of Alkaline Wastewater Research Articles

Treatment of alkaline wastewater from cleaning of color filter glass

The treatment of alkaline wastewater (noted as A-water) from cleaning of color filter glass (CFG) was studied. The A-water contains hydroxide ion and dissolved acrylic resin of high concentrations of 4 M and 80,446 mg/L chemical oxygen demand (COD), respectively. The suspended solid (SS) of A-water was removed via filtration. The effluent after filtration process (noted as F-water) was further treated via advanced oxidation processes (AOPs) such as ozonation (OZ), OZ/ultra-violet (UV) irradiation (OZ/UV) and catalytic OZ/UV with Pt/γ-Al 2O 3 (OZ/UV/Pt). The filtration process employing 0.5 μm PTFE filter yielded the F-water containing 55,749 mg/L COD with the removal efficiency of COD ( η C) relative to A-water ( η C,FA) of about 30.7% for treating the A-water. It was noted that about 33.7% COD of A-water can be also removed using the gravity sedimentation (GS). However, the GS time was as long as about 7.5 h. The values of η C relative to F-water ( η C,OF) via AOPs for treating the F-water were about 8–12% at the reaction time of 60 h. The overall η C relative to A-water ( η C,OA) can reach about 36.2–39.1% after filtration process and AOPs.

Development of a reliable alkaline wastewater treatment process: optimization of the pre-treatment step

Alkaline waters produced by caprolactam plants polymerizing the fibres of nylon-6 are characterized by a very high alkalinity, salinity and COD values, in addition to the presence of recalcitrant organic molecules. These characteristics make alkaline wastewaters very difficult to treat; so the development of the suitable sequence to carry out in a depuration process appears of great interest. The proposed general process consists of three main steps: first, pre-treatment for the acidification of the polluted stream, second, a successive extraction of the bio-recalcitrant compound (noted as cycloexanecarboxysulphonic acid (CECS)) and a final biological treatment. In particular, this paper deals with the pre-treatment step: it consists of an acidification process by means of sulphuric acid with the concomitant precipitation of black slurries in the presence of different substances, such as solvents, CaCl 2, bentonite, several flocculants and coagulants. The aim of this study is to set an experimental procedure, which could minimize fouling problems during sludge filtration. The use of additives like bentonite seems to give the best results, because it allows good COD reductions and a filterable precipitate, which avoids excessive fouling problems of the experimental apparatus.

Biological treatment of alkaline industrial waste waters

The biotechnological treatment of alkaline waste waters (AWW) resulting from the production of caprolactam by the SNIA-viscosa process has been studied. The pollutant in the AWW is 80–120 g litre −1 cyclohexanecarboxysulphonate (CECS) sodium salt with a COD up to 325 000 mg litre −1. Bacterial strains have been isolated which are able to grow on AWW and to degrade the largest possible range of organic compounds. These strains have been screened for their performance in lowering the COD and degrade the sulphonic bonds. Combinations of strains have also been verified. The strains have been compared in cultures both in shake flasks and in a laboratory scale fermenter. The results showed that: (a) a 1/10 dilution of AWW with water permitted microbial growth coupled with decrease in COD and carboxylic concentration (representative of several organic compounds such as cyclohexanecarboxysulphonate, 2-aminocapronic and ε-aminocapronic acids); (b) the polymerised caprolactam molecules are exhaustively degraded; (c) very similar results are found both in shake flask tests and in the lab scale fermenter but with different kinetics; and (d) pretreatment of alkaline waters with CaCl 2 and lowering the pH with H 3PO 4, implement the kinetics and yields of the process in terms of degradation of COD and carboxylic compounds. The experiments gave very preliminary results and led to some suggestions for the development of a chemical and biological process to treat this kind of AWW.

硫黄酸化細菌による硫化水素含有アルカリ廃水の生物学的処理

硫黄酸化細菌による硫化水素含有アルカリ廃水の生物学的処理

Treatment of Alkaline Wastewater from Lignite-Fired Power Plants

Given are characteristics of, and treatment methods for, alkaline wastewaters from the hydrotransport of the fly ash from a lignite-fired power plant. The principal component of the fly ash is CaO. The impact of this type of waste on the aquatic environment is considered. Two treatment procedures are tested - CO2 recarbonation and aeration. The aeration of alkaline wastewaters yields good treatment efficiencies, bringing about the precipitation of calcium carbonate. Determined is the relationship between the duration of the treatment process and the chemical composition of the wastewater, as well as the aeration time required to achieve the desired decrease of the alkalinity and pH levels.

Factors affecting pH change in alkaline wastewater treatment—II carbon dioxide production

The carbon dioxide produced during biological oxidation of wastewater has a pronounced influence upon the pH that is attained in the activated sludge process. The quantity produced is proportional to the COD removed, its degree of oxidation and depends also on the oxidation level of the substrate. A discussion of metabolism is given with emphasis on the description of the oxygen consumption. The theory is compared with experimental results. A mass balance for the metabolism of model compounds is presented. This model is based on a thermodynamic consideration of the metabolic process and offers a basis for calculation of R. Q. values. Experimental evidence for the applicability of this model is presented. Experimental results for a sewage are applied in pH calculations.

Chemical Neutralization of Alkaline Wastewater During Activated Sludge Treatment

Abstract The chemical neutralization of alkaline wastewater during the activated sludge treatment is due mostly to the development of CO2 during such biological treatment. The full-scale activated sludge treatment of alkaline wastewater without preliminary separate chemical neutralization was studied for the case of an unbleached Kraft pulp mill effluent. The treatment was carried out in limited-mixing aeration tanks at conventional loadings. Maximum pH values of the mixed liquor were 10.2, and the corresponding total alkalinity values reached 23.8 me/l. It was observed that considerable parts of the waste-water alkalinity were removed during the initial periods of mixed liquor aeration. The practical limit of this type of neutralization seems to be close to pH of 8.

Factors affecting pH change in alkaline waste water treatment—I

The pH of wastewater in various stages of its purification depends mainly upon the equilibria of carbonic acid. Thus relations between pH and the concentrations of carbon dioxide, bicarbonate and carbonate can be formulated. Corrections for the non-ideal character of the sewage are necessary. With some restrictions the concept of alkalinity can be used for these pH relations. Several (bio)chemical and physical processes occurring in biological purification affect the concentrations of carbon dioxide and (bi)carbonate. Processes studied are carbon dioxide desorption, oxidation of organic matter and nitrification. Models are proposed for the calculation of the effluent pH and the values so obtained are compared with the available experimental results.