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An improved approach based on the use of iron-doped polymeric beads (IPB) as Fenton catalyst in the pretreatment and biomass-doped polymeric bead (BPB) in the biological oxidation has been reported for the removal of different aromatic mixtures present as pollutants in the aqueous solutions. Degradation has been investigated at fixed loading of IPB as 2.5 % weight basis and varying loading of hydrogen peroxide so as to understand the effect of oxidant loading on the extent of degradation. It has been observed that the maximum removal efficiency as 75.5, 81.4, and 59.1 % was obtained for the benzene-toluene-naphthalene-xylene (BTNX), benzene-toluene-ethylbenzene-xylene (BTEX), and benzene-toluene-naphthalene-p-nitrophenol (BTNp-NP) mixtures, respectively, at a 40-min pretreatment and optimum pH of 3.5. The biodegradability index was also observed in the favorable range of 0.4 to 0.5 after the pretreatment at optimum H2O2 loading of 1.5 g L−1. Maximum COD removal efficiency of 99.2, 99.3, and 99.6 % was obtained using the biological oxidation treatment for 40 h for the case of BTNX, BTEX, and BTNp-NP mixtures, respectively. Analysis of kinetic models revealed that degradation followed three distinct stages based on fitting of the three-stage model and BPB was found to be more efficient as compared to the primary activated sludge (PAS) and modified activated sludge (MAS). Reusability studies confirmed that both IPB and BPB were effective over many cycles giving stable performance during degradation without leaching of Fe3+ ions into the solution.

The biosorption potential of modified sludge biomass (MSB) immobilized by various mechanisms was investigated for removal of Cu(II) and Cr(VI) metals. The sorption efficiency (mg g −1 ) decreased in the order Polyvinylalcohol-carboxymethylcellulose sodium salt-activated carbon (PVA-CMC-AC) > Polyvinylalcohol-carboxymethylcellulose sodium salt (PVA-CMC) > Polyvinylalcohol (PVA) > calcium alginate (CA) under the optimized operating conditions as pH of 5.0, metal concentration of 0.1 g L −1 , adsorbent loading as 0.1 g MSB/100 mL and treatment time of 85 min as established in the work. The equilibrium data fitted well with Langmuir isotherm model and pseudo first order kinetic model. 20% CaCl 2 was established as best eluting agent and the regenerated adsorbent can be used in 5 cycles with marginally reduced efficacy.

It was reported by us in 2018 that phosphate fertilizers marketed in India are contaminated with fluoride (0.85 % w/w on average). A follow-up study conducted in 2019 did not reveal any improvement in the situation. It is reported herein that 57–89 % w/w residual fluoride in as-received single superphosphate (SSP) powder samples could be removed through thermal treatment at 140 ± 5 °C. Fluoride removal was ascribed to formation and escape of gaseous acidic fluoride constituents, with concomitant increase in the fertilizer pH from 4.7-5.8 to 6.0–6.5. The pH increase was likely due to a shift of the H 2 P O 4 - ⇌ H P O 4 2 - equilibrium to the right. A marginal reduction in the sample mass (4.2–10.2 % w/w) was also observed. Similar thermal treatment given to as-received granular diammonium phosphate (DAP) samples reduced the fluoride content by 57–93 % w/w. The reduction was ascribed to removal of ( N H 4 ) 2 S i F 6 , which has lower decomposition temperature than DAP. The pH of the DAP samples reduced from 8.2–8.5 to 6.5–7.7, the sample mass reduced by 7.4–16.6 % w/w, and in one sample subjected to N, P analysis, the N/P ratio reduced from 1.16 to 0.71. These observations were consistent with a partial loss of ammonia and a shift of the H P O 4 2 - ⇌ H 2 P O 4 - equilibrium to the right. Exposure of a heat-treated DAP fertilizer to ammonia vapour raised the pH to 8.1. This suggested that, if fluoride impurities can be separated out from the gaseous emission released on thermal treatment, the lost ammonia can, in principle, be recycled to regenerate the original DAP through gas-solid reaction.

Improved biological oxidation based on pretreatment using combined Fenton and ultrasound in presence of stirring as the best approach and use of modified activated sludge was demonstrated for the treatment of wastewater containing benzene, toluene, naphthalene and o-xylene. The optimum pretreatment conditions were observed as initial pH of 3–3.5, Fe 2+ dosage of 2.0 g L –1 and H 2 O 2 dosage of 1.0 g L –1 giving about 80–95% reduction in the chemical oxygen demand (COD) and favorable BOD 5 /COD value for the biological oxidation. Use of modified prepared activated sludge gave about 20–30% higher extent of degradation as compared to the conventional sludge types.

The treatment of a synthetically prepared wastewater containing ethylbenzene and p-nitrophenol has been investigated using combined treatment schemes based on the advanced oxidation process followed by the conventional aerobic oxidation process (using primary activated sludge (PAS), modified prepared activated sludge (MPAS) based on the use of combined sludge from different treatment sources and activated sludge (AS)). The operating conditions for the pretreatment scheme have been optimized and it has been observed that initial pH of 3–3.5, a Fe2+ dosage of 2.0 g L−1 and a H2O2 dosage of 1.5 g L−1 in combination with ultrasound gives the best performance. Approximately, 55–70% reduction in the chemical oxygen demand (COD) was obtained at optimum conditions after pretreatment from initial conditions of COD as 3642 and 3417 mg L−1 and BOD as 881 and 533 mg L−1 for the wastewater containing ethylbenzene and p-nitrophenol respectively. From an initial BOD5/COD (BI) value of around 0.15–0.2, the ratio was found to increase to about 0.30–0.35 after pretreatment, which is considered good for the aerobic treatment. In the case of aerobic oxidation, promising results were obtained for the modified prepared activated sludge giving better conversion ability of intermediates into solid residue and higher biomass yield that could be separated by simple filtration as compared to the primary activated or the activated sludge treatment. The best treatment approach as established in the work was ultrasound assisted Fenton process as the pretreatment followed by biological oxidation using MPAS.

The present work reports the preparation of modified activated sludge (MAS) with isolation studies and performance evaluation for the removal of aromatic pollutants. On the basis of biochemical and physiological characteristics study, about 389 bacterial isolates (combination of gram-negative and gram-positive) were identified in the sludge. Performance evaluation studies for treatment of wastewater containing aromatic pollutants using modified activated sludge revealed that a maximum of 67% reduction in the pollutant loading was obtained for only biological process which significantly increased to 98% for the combined process of Fenton treatment and biological oxidation. Improved biodegradability was also observed with BOD5/COD value of about 0.30–0.35 with pretreatment time of 40 min for effluent containing benzene, toluene, naphthalene and xylene and 60 min for effluent containing ethylbenzene and p-nitrophenol. Comparison of the performance of MAS with the more commonly used prepared activated sludge and the activated sludge process revealed superior degradation effectiveness and growth characteristics. Kinetic studies also revealed that maximum substrate reduction with enhanced microbial growth of bacterial strain was obtained for MAS. Overall the present work has clearly highlighted the novelty of using a modified activated sludge based on the mixed culture of microorganisms and the better efficacy of the combined treatment scheme based on Fenton’s oxidation and biological oxidation using MAS.

BACKGROUND Improvements in biological oxidation approaches are required due to significant problems associated with this simple and commonly used approach. The work presents use of immobilized modified prepared activated sludge using modified polyvinyl alcohol (PVA)-alginate beads for removal of BTX and modifications based on the use of Fenton chemistry as pretreatment scheme. RESULTS Improved synthesis processes for immobilized sludge beads have been developed based on understanding the effect of PVA and alginate loadings. Stable beads with high levels of sludge activity were shown to give similar levels of COD removal efficiency compared with free sludge. In the case of Fenton pretreatment, 40 min of treatment was found to increase BOD5:COD value to about 0.31. Maximum COD efficiency of 93.1% was obtained using a biological process on a Fenton-treated sample which is significantly higher than that obtained with the untreated sample. The immobilized sludge was reused over nine batches without substantial loss in BTX degradation ability. Kinetic studies have also been presented. CONCLUSION An improved and promising approach for treatment of BTX containing wastewater with proven efficacy of the bioactivity and mechanical stability of the immobilized sludge, has been presented with better results based on Fenton pretreatment. © 2014 Society of Chemical Industry