Increase In Hydraulic Retention Time Research Articles

Removal of Pb 2+ and Ni 2+ by bio-sludge in sequencing batch reactor (SBR) and granular activated carbon-SBR (GAC-SBR) systems

Living bio-sludge from domestic wastewater treatment plant was used as adsorbent of heavy metals (Pb 2+, Ni 2+) and its adsorption capacity was about 10–30% reduced by autoclaving at 110 °C for 10 min. The living bio-sludge acclimatized in synthetic industrial estate wastewater (SIEWW) without heavy metals showed the highest Pb 2+ and Ni 2+ adsorption capacities at 840 ± 20 and 720 ± 10 mg/g bio-sludge, respectively. The adsorbed Pb 2+ and Ni 2+ were easily eluted (70–77%) from bio-sludge by washing with 0.1 mol/l HNO 3 solution. The heavy metals (Pb 2+, Ni 2+) removal efficiency of both SBR and GAC-SBR systems were increased with the increase of hydraulic retention time (HRT), or the decrease of organic loading. The SBR system showed higher heavy metals removal efficiency than GAC-SBR system at the same organic loading or HRT. The Pb 2+, Ni 2+, BOD 5, COD and TKN removal efficiencies of GAC-SBR system were 88.6 ± 0.9%, 94.6 ± 0.1%, 91.3 ± 1.0%, 81.9 ± 1.0% and 62.9 ± 0.5%, respectively with industrial estate wastewater (IEWW) with 410 mg/l glucose, 5 mg/l Pb 2+ and 5 mg/l Ni 2+under organic loading of 1.25 kg BOD 5/m 3 d (HRT of 3 days). The bio-sludge quality (sludge volume index: SVI) of the system was less than 80 ml/g. The excess sludge from both SBR and GAC-SBR systems with SIEWW under the organic loading of 1.25–2.50 kg BOD 5/m 3 d contained Pb 2+ and Ni 2+ at concentrations of 240–250 mg Pb 2+/g bio-sludge and 180–210 mg Ni 2+/g bio-sludge, respectively.

Aerobic digestion of starch wastewater in a fluidized bed bioreactor with low density biomass support

A solid–liquid–gas, multiphase, fluidized bed bioreactor with low density particles was used in this study to treat the high organic content starch industry wastewater. The characteristics of starch wastewater were studied. It shows high organic content and acidic nature. The performance of a three phase fluidized bed bioreactor with low density biomass support was studied under various average initial substrate concentrations, by varying COD values (2250, 4475, 6730 and 8910 mg/L) and for various hydraulic retention times (8, 16, 24, 32 and 40 h) based on COD removal efficiency. The optimum bed height for the maximum COD reduction was found to be 80 cm. Experiments were carried out in the bioreactor at an optimized bed height, after the formation of biofilm on the surface of low-density particles (density = 870 kg/m 3). Mixed culture obtained from the sludge, taken from starch industry effluent treatment plant, was used as the source for microorganisms. From the results it was observed that increase in initial substrate concentration leads to decrease in COD reduction and COD reduction increases with increase in hydraulic retention time. The optimum COD removal of 93.8% occurs at an initial substrate concentration of 2250 mg/L and for the hydraulic retention time of 24 h.

Application of membrane-coupled anaerobic volatile fatty acids fermentor for dissolved organics recovery from coagulated raw sludge

To investigate the treatment performance of membrane-coupled anaerobic volatile fatty acids fermentor system, the effects of operational parameters for volatile fatty acids production were evaluated through experiments and a mathematical model. The volatile fatty acids recovery ratio was largely affected by the change of hydraulic retention time, reaching its maximum value at 12 hrs. Over the range of hydraulic retention time 8 to 96 hrs, the volatile fatty acids recovery ratio decreased with the increase of hydraulic retention time above 12 hrs, while the ratio of mineralization and gasification increased. Hydraulic retention time and membrane filtration ratio should be maintained less than 1 day and above 0.9, respectively, to attain over 40% of organic materials recovery ratio at 10 days of solids retention time. When the hydrolysis rate constant was 0.01 hr-1, the organic loading rate should be maintained at above 1.0 (kgC/m3/day) to attain over 45% of volatile fatty acids recovery ratio. Based on experimental and simulated results, membrane-coupled anaerobic volatile fatty acids fermentor system was thought to be effective for dissolved organics recovery from coagulated sewage sludge.

The Acid-Phase Anaerobic Digestion of Primary Sludge and Its Role in the Biological Phosphorus Removal Process

Abstract The effects of certain operational and environmental parameters on the acid-phase anaerobic digestion of primary sludge have been investigated using a series of bench-scale, continuous-flow experiments. Short-chain volatile fatty acids (VFA), the main products of the process, are preferred substrates for the bacteria involved in the biological removal of phosphorus. Results show that the net volatile fatty acid generation improves with an increase in hydraulic retention time (up to 12 hours) as well as in solids retention time. Although acid production is not affected by a decrease in pH from 5.1 to 4.5, the production is significantly lower (25 to 30%) at pH of about 6.0. The use of different feed sources influences to some extent the amount of product formation. Moreover, lipid and carbohydrate degradation patterns are dependent on reactor configuration, whereas protein utilization appears to be independent of the reactor regime. The amount of VFA produced, in most cases, is high enough to support biological phosphorus removal processes.