The effect of initial pH and retention time on boron removal by continuous electrocoagulation process

In this study, factors influencing boron removal via the continuous electrocoagulation process were investigated at lab-scale. Different influent pH values (4, 5, 6, 7.45 and 9) and contact times (10, 25, 50 and 100 min) were examined as variable parameters. Plate-type aluminium electrodes with 5 mm distance between them were used. All the experiments were conducted in continuous mode and the current density was kept constant at 5 A throughout the whole experimental period. The initial boron concentration was selected to be 1000 mg L-1. The first set of experiments concerning the influence of the influent pH showed that the highest boron removal (67%) was obtained at pH=6 since it was the optimal pH for boron precipitation through aluminium borate formation. Under the constant current density of the study and with the initial pH adjusted to 6, increasing the duration of the electrocoagulation process from 10 to 100 min resulted in raising the boron removal from 45 to 79% during the second set of experiments. The greater duration of the electrocagulation process enabled higher aluminium dissolution, thus allowing the existence of a higher number of coagulants within the reactor. Moreover, it enhanced boron precipitation because of the longer contact time between the boron ions and the coagulants. After optimizing significant parameters such as the influent pH and the electrocagulation duration, the continuous electrocoagulation process was found to constitute an effective alternative for boron removal

Removal of endocrine disrupting compounds in a lab-scale anaerobic/aerobic sequencing batch reactor unit

The fate and removal of six selected endocrine disrupting compounds in a lab-scale anaerobic/aerobic (A/O) sequencing batch reactor (SBR), operating at 5 days, solids retention time (SRT) were investigated. A carbamazepine (CBZ), acetaminophen (ATP), diltiazem (DTZ), butyl benzyl phthalate (BBP), estrone and progesterone mix was spiked as model endocrine disrupting compounds (EDC) into domestic wastewater obtained from a nearby sewage treatment plant. The influent, effluent and sludge samples from the SBR unit were analysed by using an LC/MS/MS instrument equipped with electrospray ionization. More than 80% removal was observed for all the EDCs tested. It was found that biodegradation is the most important mechanism for BBP, ATP and progesterone. Biodegradation constants were calculated according to the simplified Monod model for these compounds. The DTZ seemed to have lower rate of biodegradation. The CBZ appeared totally resistant to biodegradation. However, it presented a high rate of sorption onto the sludge and was thereby treated. This contradicts with the literature studies

An ozone assisted process for treatment of EDC's in biological sludge

A novel aerobic sludge digestion process to stabilize and decrease the amount of excess sludge produced during biological treatment and removal of EDCs sorbed onto sludge during this process is discussed here. Waste activated sludge samples from two different wastewater treatment plants were ozonated for different periods in Erlenmeyer flasks once a day on each of four consecutive days. Flasks were continuously aerated between ozone applications by shaking on an orbital shaker. The residual EDC concentrations in sludge samples were analyzed at the end of digestion periods. An MLVSS reduction of up to 95% was achieved with an ozone dose of only 1.05 g O-3/kg MLSS in this process on the fourth day. During this process destruction of some selected endocrine disrupting compounds, namely diltiazem, carbamazepine, butyl benzyl phthalate, acetaminophen and two natural hormones, estrone and progesterone, which tend to accumulates in sludge, are studied. Over 99% removal of these contaminants were achieved at the end of the fourth day. The analyses were conducted by using LC (ESI) MS/MS after solid phase extraction (SPE). By this process it became possible to save on contact time as well as achieving a bio-solids digestion far exceeding the standard aerobic process and concomitant removal of micropollutants at the expense of minimum ozone dose. The developed process is deemed superior over side-stream ozonation of activated sludge, in that it does not cause reduction in active biomass in the aeration tank