Electron donor addition for stimulating the microbial degradation of 1,4 dioxane by sequential batch membrane bioreactor: A techno-economic approach.

The presence of 1,4 dioxane in wastewater is associated with severe health and environmental issues. The removal of this toxic contaminant from the industrial effluents prior to final disposal is necessary. The study comprehensively evaluates the performance of sequential batch membrane bioreactor (MBR) for treating wastewater laden with 1,4 dioxane. Acetate was supplemented to the wastewater feed as an electron donor for enhancing and stimulating the microbial growing activities towards the degradation of 1,4 dioxane. The removal efficiency of 1,4 dioxane was maximized to 87.5 ± 6.8% using an acetate to dioxane (A/D) ratio of 4.0, which was substantially dropped to 31.06 ± 3.7% without acetate addition. Ethylene glycol, glyoxylic acid, glycolic acid, and oxalic acid were the main metabolites of 1,4 dioxane biodegradation using mixed culture bacteria. The 1,4 dioxane degrading bacteria, particularly the genus of Acinetobacter, were promoted to 92% at the A/D ratio of 4.0. This condition encouraged as well the increase of the main 1,4 dioxane degraders, i.e., Xanthomonadales (12.5%) and Pseudomonadales (9.1%). However, 50% of the Sphingobacteriales and 82.5% of Planctomycetes were reduced due to the inhibition effect of the 1,4 dioxane contaminate. Similarly, the relative abundance of Firmicutes, Verrucomicrobia, Chlamydiae, Actinobacteria, Chloroflexi, and Nitrospirae was reduced in the MBR at the A/D ratio of 4.0. The results derived from the microbial analysis and metabolites detection at different A/D ratios indicated that acetate supplementation (as an electron donor) maintained an essential role in encouraging the microorganisms to produce the monooxygenase enzymes responsible for the biodegradation process. Economic feasibility of such a MBR system showed that for a designed flow rate of 30 m3∙d-1, the payback period from reusing the treated wastewater would reach 6.6 yr. The results strongly recommend the utilization of mixed culture bacteria growing on acetate for removing 1,4 dioxane from the wastewater industry, achieving dual environmental and economic benefits.

Treatment of hazardous wastewater generated from metal finishing and electro-coating industry via self-coagulation: Case study.

The aim of this study is to find out a sustainable and cost-effective solution to manage hazardous shock loads from metal finishing and electro-coating industry. Results indicated that the main sources of hazardous wastewater are coming from batch chemical cleaning of degreasing basin (CCDB) (pH 13) and contains very hazardous chemicals, batch chemical cleaning of phosphating basin (CCPB) (pH 1.03) and contains high concentrations of iron (2300 mg/L) and zinc (2400 mg/L) and degreasing basin contents (DBC). Different treatment approaches were investigated. Results indicated that mixing CCDB with CCPB at their actual discharge allowed to form a self-coagulant of metal hydroxide which was utilized to treat the (DBC) followed by sedimentation. Removal efficiency of COD (87%), TSS (94%), and oil and grease (92%) were achieved. To compare the efficiency of this treatment approach, conventional chemical coagulation of DBC was carried out using FeCl3 but the amount was very high. In conclusion, results proved the advantage of using self-coagulation to treat DBC since it eliminates the use of external chemicals and provides an integrated solution for the three main sources of hazardous pollutants. PRACTITIONER POINTS: The manuscript provide an innovative and sustainable solution to the shock loads of hazardous wastewater generated from metal finishing and E-coating industry by utilizing iron-rich wastewater from chemical cleaning of phosphating basin and alkaline wastewater from chemical cleaning of degreasing basin to produce metal hydroxide. The metal hydroxide was cost-effective and technically effectively than external coagulant in treating highly polluted degreasing basin content at due discharge time. Iron-rich wastewater could be used to produce self-coagulant of iron hydroxide. Mixing iron rich wastewater and alkaline wastewater produce iron hydroxide. Iron hydroxide is cost-effective in treating hazardous wastewater of degreasing basin.

Performance of aerated submerged biofilm reactor packed with local scoria for carbon and nitrogen removal from municipal wastewater.

An up-flow submerged biofilm reactor packed with scoria was evaluated for municipal wastewater treatment. The reactor was operated two cycles (with and without effluent recycle) as single aerobic reactor at hydraulic loading rate (HLR) of 3.5-4.0 L/L/day and four cycles (with and without effluent recycle) as anaerobic/aerobic reactor at two HLR (3.5 and 5.2 L/L/day). Results indicated better removal efficiency in case of anaerobic/aerobic cycles especially for ammonia and total nitrogen. Effluent recycling in the aerobic reactor enhanced ammonification with significant reduction in ammonia and nitrogen removal, while in case of single anaerobic/aerobic reactor the effluent recycling improved ammonia and nitrogen removal and kept nitrate concentration in the final effluent below 10 mg N/L. The reactor produced good settled sludge with sludge volume index (SVI) of 46-74 ml/g for aerobic cycles and 18-50 ml/g for anaerobic/aerobic cycles. The average sludge production was 0.145 g TSS/g COD removed.

Resource recovery from septic tank effluent using duckweed-based tilapia aquaculture.

Two parallel duckweed ponds were deployed to utilize nutrients from the effluent of a septic tank treating domestic wastewater. The effluent and fresh biomass of duckweed pond were fed to two subsequent fish ponds stocked with Nile tilapia (Oreochromis niloticus). Fish ponds receiving freshwater and commercial feed were used as control. The results of specific growth rate and feed conversion ratio showed no significant difference between the control ponds and treatment ponds. On the other hand, the total and net fish yields were significantly higher in the control. Microbial analysis revealed contamination of gills, intestine and liver of fish in the treatment ponds. The activity of the immune response genes was up-regulated in the brain and liver of the treatment samples. A micronucleus assay revealed a similar percentage of micronuclei in the polychromatic erythrocytes of blood in the control and treatment samples, while the treatment samples a had higher incidence of micronuclei in the polychromatic erythrocytes of gills, compared with the control.

Use of cloth-media filter for membrane bioreactor treating municipal wastewater.

This study evaluated three different textile materials (Acrylate, Polyester, and Nylon) as filter media for MBR treating municipal wastewater. Chemical oxygen demand (COD) loading rates were 1.71, 1.65 and 1.84 g/l d while feed/microorganisms (F/M) ratios were 0.32, 0.31 and 0.33 in Reactor 1, Reactor 2 and Reactor 3, respectively. The actual hydraulic retention times were 8.6, 8.9 and 8.0 h in R1, R2 and R3. At 5.3-5.5 g/l mixed liquor suspended (MLSS) and 26.3 days solid retention time (SRT) the membrane bioreactors were effective in removing 93-95% of COD, 99% of total suspended solids (TSS) and turbidity, 89-94% of total kjeldahl nitrogen (TKN) and 90-96% of total ammonia nitrogen. Phosphorous removal was limited to 51-55% while faecal coliform was reduced by four logs. Quality of the treated effluents met both Saudi and Egyptian reuse standards for restricted irrigation and could be easily disinfected to meet the unrestricted irrigation standards.

Nutrient recovery from domestic wastewater using a UASB-duckweed ponds system.

The pilot-scale wastewater treatment system used in this study comprised a 40-l UASB reactor (6-h HRT) followed by three duckweed ponds in series (total HRT 15 days). During the warm season, the treatment system achieved removal values of 93%, 96% and 91% for COD, BOD and TSS, respectively. Residual values of ammonia, TKN and total phosphorus were 0.41 mg N/l, 4.4 mg N/l and 1.11 mg P/l, with removal efficiencies of 98%, 85% and 78%, respectively. The system achieved 99.998% faecal coliform removal during the warm season with final effluent containing 4 x 10(3) cfu/100 ml. During the winter, the system was efficient in removing COD, BOD and TSS but not nutrients. The system was deficient in the removal of faecal coliforms during the winter, producing effluent with 4.7 x 10(5) cfu/100 ml. During the warm season, the N removal consisted of 80% by plant uptake, 5% by sedimentation and 15% unaccounted for. A duckweed production rate of 33 t dry matter per hectare per 8 months was achieved.

Microbial quality of tilapia reared in fecal-contaminated ponds.

The microbial quality of tilapia reared in four fecal-contaminated fishponds was investigated. One of the fishponds (TDP) received treated sewage with an average fecal coliform count of 4 x 10(3)cfu/100mL, and feed of fresh duckweed grown on treated sewage was used. The number of fecal coliform bacteria attached to duckweed biomass ranged between 4.1 x 10(2) and 1.6 x 10(4)cfu/g fresh weight. The second fishpond (TWP) received treated sewage, and the feed used was wheat bran. The third fishpond (FDP) received freshwater, and the feed used was the same duckweed. Pond 4 (SSP) received only settled sewage with an average fecal coliform count of 2.1 x 10(8)/100mL. The average counts in the fishponds were 2.2 x 10(3), 1.7 x 10(3), 1.7 x 10(2), and 9.4 x 10(3)cfu/100mL in TDP, TWP, FDP, and SSP, respectively. FDP had a significantly (P < 0.05) lower fecal coliform count than the treated sewage-fed ponds and SSP. The microbial quality of the tilapia indicated that all tissue samples except muscle tissues were contaminated with fecal coliform. Ranking of the fecal coliform contamination levels showed a decrease in the order intestine>gills>skin>liver. Poor water quality (ammonia and nitrite) in SSP resulted in statistically higher fecal coliform numbers in fish organs of about 1 log(10) than in treatments with good water quality. Pretreatment of sewage is therefore recommended.