Volume 20 [2018]

The discharge of colored textile wastewaters containing dyes with different chemical characteristics into the receiving streams is a problem for toxicological, ecological and also esthetical reasons. Most of dyes are stable, and not easily degradable by the conventional treatment methods, so removal of dyes from the textile effluents is a major problem. This study aimed to investigate color removal efficiency of two aerobic filter column reactors operated as sequencing as biological and chemical treatment steps. Biological column reactor (BR) filled with basaltic lava (Scoria) as supporting media for microorganisms, and second column reactor (CR) was filled with lime and textile fly ash mixture (1:3, w/w) used as chemical treatment step especially for phosphate and color removal. The reactors were operated at batch mode to investigate the effect of hydraulic retention times (HRT), aeration time and initial dye concentration (Everzol Blue BB) on treatment efficiencies. The results of the study showed that this system has quite high removal efficiencies for soluble organics and nutrients from wastewater. COD, TOC, NH4-N and PO4-P removal rates were obtained as 94.2 %, 94.8 %, 84.7 % and 97.5% in HRT of 24 h, respectively. In addition, this two-step treatment system reached to quite high color removal efficiencies of 96.4 % Pt/Co, 96.4 % DFZ-436 nm, 99.5 % DFZ-525 nm, and 99.8 % DFZ-620 in initial dye concentration of 800 ppm.

A wide range of technologies has been developed for the removal of dyes from wastewaters to decrease their environmental impact. Wastewater containing dyes is generally treated using more than one process such as adsorption/biosorption. In this study, effects of initial pH (2-8), initial azo dye concentration (Co:25-200 mg/l), contact time (tc:2.5-1440 min) and amount of waste sludge (m:1-15 g/l) were studied by natural and modified dried waste aerobic sludge (WS) in a lab-scale batch study and also optimized by employing response surface methodology (RSM)-Box-Behnken Model for Maxilon Red GRL(MRGRL) and Everzol Red (ER) removal from wastewaters. The optimum experimental conditions were found to be pH=5, Co= 112.5 mg/l, tc= 180 min. and m= 15g/l for dyes and MRGRL and ER removal was determined as about 97% and 95.85%, respectively. The results clearly showed that amount of WS and contact time are the most important parameters for color removal.
FTIR and SEM (scanning electron microscope) images were used to understand morphology and structural character of WS and after biosorption process. D-R biosorption isotherm model was used in order to determine type of biosorption mechanism. The E value of D-R isotermisotherm model was found to be 7.071 for both dye. Pseudo-second order and intraparticle diffusion (Weber-Morris) models were suitable for biosorption kinetics. 0,1 M HCl and NaOH were used for desorption studies. Effect of ionic strength (NaCl) was not observed between 0,5-1 mol/L NaCl on to biosorption efficiency. WS (biowaste), Natural or modified, one of the low-cost biosorbent, can be used for removal of azo dye from wastewaters.

Protozoa play a significant role in activated sludge systems, since they graze on dispersed bacteria, supporting a healthy food web in the activated sludge artificial ecosystem. However, operational parameters and influent properties are the most important factors affecting the composition of activated sludge microfauna. The objective of this study was the assessment of the treatment efficiency and the protozoan populations in activated sludge systems with and without the addition of polyvinyl alcohol (PVA) gel beads while treating wastewater in the presence of phenol. Six activated sludge reactors - 3 of them supplied with PVA gel beads –were used for the treatment of synthetic wastewater influent containing phenol at concentrations up to 10 mg/L. During the treatment of synthetic wastewater, dominance of the sessile species was observed mainly in the reactors supplied with PVA beads. Physicochemical analyses of the effluent indicated good efficiency of reactors supplied with PVA beads in removing nutrients and organic load. Introduction of phenol in the influent at a concentration of 5 mg/L did not affect significantly the operation of the reactors and the composition and abundance of activated sludge microfauna, while a high phenol removal rate was observed. The increase of influent phenol concentration to 10 mg/L resulted to the formation of foam on the surface of the reactors and the presence of Zoogleasp, while an increase was observed in the abundance of crawling species in activated sludge and PVA supplied reactors respectively.

Response surface methodology has been used to design experiments and to optimize the effect of independent variables responsible for higher adsorption of humic substances by activated carbon supported nanoscale zero-valent iron from aqueous solutions. The variables of initial concentration, time, pH, adsorbent dose was examined. The characterization of NZVI/AC was carried out by SEM-EDS and XRD analysis. The adsorption isotherms and kinetics of humic substances on AC and NZVI/AC were studied. The findings showed that the particle size of synthesis NZVI were in the range 20-50nm. The experimental data followed the Langmuir isotherm and pseudo-second kinetic model. For AC, optimum conditions of initial concentration, pH, contact time, and adsorbent dose were 5 mg L-1, 4.43, 46.28 min, and 1.5 g L-1, respectively. For NZVI/AC, optimum conditions of initial concentration, pH, contact time, and adsorbent dose were 5.48 mg L-1, 5.44, 44.7 min, 0.65 g L-1, respectively. Predicted removal efficiency by Box-Benken models for activated carbon and NZVI were 60 and 100 percent, respectively.