Effect of sludge age on performance of an activated sludge unit treating 2,4 dichlorophenol-containing synthetic wastewater

Wastewaters containing chlorophenol compounds are difficult to treat by biological means because of toxic effects of chlorophenols on microorganisms. Synthetic wastewater containing 2,4 dichlorophenol (DCP) was biologically treated in an activated sludge unit at different sludge ages varying between 5 and 30 days while the feed COD, DCP contents and hydraulic residence time (HRT) were constant. Effects of sludge age on COD, DCP and toxicity removals were investigated. Increases in sludge age caused significant increases in biomass concentration in the aeration tank, which resulted in increases in percent COD, DCP and toxicity removals. COD removal increased from 58 to 90%, while DCP and toxicity removals increased from 15 to 100% and from 38 to 100%, respectively, when the sludge age was raised from 5 to 30 days. Resazurin method based on dehydrogenase activity was used for assessment of the feed and effluent wastewater toxicity. Sludge volume index (SVI) decreased with increasing sludge age indicating improved settling characteristics of the sludge at high sludge ages. Operation at a sludge age of 25 days resulted in more than 90% COD and nearly 100% DCP and toxicity removal with an SVI value of 108 ml g⁻¹ under the experimental conditions tested.     

Decolorization of Reactive Red 195 by a mixed culture in an alternating anaerobic–aerobic Sequencing Batch Reactor

The mono-azo dye Reactive Red 195 (RR 195) is a widely used color compound in the textile industry. As many other colors, it is persistent and difficult to be removed from water with conventional processes. The present study investigates biological decolorization of RR 195 under alternate anaerobic–aerobic conditions in a laboratory scale Sequencing Batch Reactor (SBR) containing a mixed culture and fed with a biodegradable carbon source. Different values of the Sludge Retention Time (SRT), Hydraulic Retention Time (HRT), influent color and organic carbon loadings were adopted during the experimental activity and their effects on color and Chemical Oxygen Demand (COD) removal efficiencies and process kinetics determined. The optimal operating conditions were found to be: 800 mg l⁻¹ influent COD, 50 d SRT and a 24 h-cycle. Under these conditions, the maximum color efficiency of 97% was achieved for a 40 mg l⁻¹ RR 195 in the feed. Some inhibition was present at influent color loadings above 40 mg l⁻¹, which was confirmed by the application of the Haldane model.     

Effects of nitrobenzene concentration and hydraulic retention time on the treatment of nitrobenzene in sequential anaerobic baffled reactor (ABR)/continuously stirred tank reactor (CSTR) system

The effects of increasing nitrobenzene (NB) concentrations and hydraulic retention times (HRT) on the treatment of NB were investigated in a sequential anaerobic baffled reactor (ABR)/aerobic completely stirred tank reactor (CSTR) system. In the first step of the study, the maximum COD removal efficiencies were found as 88% and 92% at NB concentrations varying between 30 mg L^?1 and 210 mg L^?1 in ABR. The minimum COD removal efficiency was 79% at a NB concentration of 700 mg L^?1. The removal efficiency of NB was nearly 100% for all NB concentrations in the ABR reactor. The methane gas production and the methane gas percentage remained stable (1500 mL day^?1 and 48–50%, respectively) as the NB concentration was increased from 30 to 210 mg L^?1. In the second step of the study it was found that as the HRT decreased from 10.38 days to 2.5 days the COD removal efficiencies decreased slightly from 94% to 92% in the ABR. For maximum COD and NB removal efficiencies the optimum HRT was found as 2.5 days in the ABR. The total COD removal efficiency was 95% in sequential anaerobic (ABR)/aerobic (CSTR) reactor system at a minimum HRT of 1 day. When the HRT was decreased from 10.38 days to 1 day, the methane percentage decreased from 42% to 29% in an ABR reactor treating 100 mg L^?1 NB. Nitrobenzene was reduced to aniline under anaerobic conditions while aniline was mineralized to catechol with meta cleavage under aerobic conditions.     

Thermophilic treatment of bulk drug pharmaceutical industrial wastewaters by using hybrid up flow anaerobic sludge blanket reactor

The hybrid up flow anaerobic sludge blanket reactor was evaluated for efficacy in reduction of chemical oxygen demand (COD) and biochemical oxygen demand (BOD) of bulk drug pharmaceutical wastewater under different operational conditions. The start-up of the reactor feed came entirely with glucose, applied at an organic loading rate (OLR) 1 kg COD/m³ d. Then the reactor was studied at different OLRs ranging from 2 to 11 kg COD/m³ d with pharmaceutical wastewater. The optimum OLR was found to be 9 kg COD/m³ d, where we found 65–75% COD and 80–94% of BOD reduction with biogas production containing 60–70% of methane and specific methanogenic activity was 320 ml CH₄/g-VSS d. By the characterization studies of effluent using GC–MS, the hazardous compounds like phenol, l,2-methoxy phenol, 2,4,6-trichloro phenol, dibutyl phthalate, 1-bromo naphthalene, carbamazepine and antipyrine were present. After the treatment, these compounds degraded almost completely except carbamazepine. Thermophilic methanothrix and methanosaetae like bacteria are present in the granular sludge.     

Investigation on the formation and kinetics of glucose-fed aerobic granular sludge

Aerobic granular sludge was cultivated in a glass sequencing batch reactor (SBR) with glucose synthetic wastewater. The spherical shaped granules were observed on 4th day with the mean diameter of 0.1 mm. With the increase of chemical oxygen demand (COD) concentration of the influent, aerobic granules grew matured, the size of which ranged from 1.2 to 1.9 mm. The aerobic granular sludge could sustain high organic loading rate (about 4.0 g COD L⁻¹ d⁻¹), with good settling ability (settling velocity 36 m/h) and high biomass concentration (MLSS 6.7 ±0.2 g/L). Experimental data indicated that the substrate utilization and biomass growth kinetics followed Monod's kinetics model approximately. The corresponding kinetic coefficients of maximum specific substrate utilization rate (k), half velocity coefficient (K_s), growth yield coefficient (Y) and decay coefficient (K_d) were 13.2 d⁻¹, 275.8 mg/L, 0.183–0.250 mg MLSS/mg COD and 0.023–0.075 d⁻¹, respectively, which made aerobic granules have short setup period, high rate of substrate utilization and little surplus sludge.     

Prefermentation to overcome nutrient limitations in food processing wastewater: Comparison of pilot- and bench-scale systems

A bench- and a pilot-scale anaerobic/aerobic system were evaluated for the treatment of high strength tomato-processing wastewater. The pilot-scale anaerobic tank achieved better prefermentation of organic carbon and nitrogen than the bench-scale system, although overall system performance was comparable with more than 99% SBOD removal and 97% SCOD removal. Hydraulic retention time (HRT) and temperature effects were studied in the bench-scale system. Increase of anaerobic HRT from 0.25 day to 0.5 day favored prefermentation and a better effluent quality was achieved, as demonstrated by reduction in TSS concentrations from 66 mg/L to 24 mg/L, SCOD from 103 mg/L to 78 mg/L and SBOD from 8 mg/L to 6 mg/L, respectively. Specific oxygen uptake rate (SOUR) increased from 0.15–0.23 mg O₂/mg VSS day at 25 °C to 0.67–1.24 mg O₂/mg VSS day at 32 °C. Settling characteristics deteriorated from sludge volume index (SVI) of 24–131 mL/g at 25 °C to 115–173 mL/g at 32 °C. Sludge yield decreased from 0.14 g VSS/g COD at 25 °C to 0.098 g VSS/g COD at 32 °C.     

A key cultivation technology for denitrifying granular sludge

Well-formed denitrifying granular sludge with a biomass concentration of 24.8 gVSS L^?1 and a specific nitrate removal rate of 0.19 gNO₃-N gVSS^?1 d^?1 was obtained in an upflow sludge blanket (USB) reactor by cultivating seeded aerobic flocculent sludge for 6–8 weeks. Regularity phenomena exist in the granulation including flotation of flocculent sludge, formation of fine granules, occurrence of channelling, and formation of mature granular sludge. The granulation is similar to crystal growth, that the non-denitrifying bacteria evolve into the carriers (fine granules), on the surface of which denitrifying bacteria proliferate and develop into mature granular sludge.There are several key parameters that must be considered when developing a good denitrifying granular sludge. First, the proper seed sludge must be chosen (VSS/SS at 0.65–0.75, SRT over 25 days) to accelerate the granulation process. Secondly, any floating sludge should be stirred, and the sludge loading rate should be within the range of 0.05–0.15 gNO₃-N gVSS^?1 d^?1 until fine granules emerge. Additionally, spontaneous gas agitation or interval air-blowing should be used to effectively eliminate channelling; Finally, the sludge loading rate should be less than 0.25 gNO₃-N gVSS^?1 d^?1 until dense, mature granular sludge appears. This study could support and promote the full-scale application of denitrifying granular sludge.     

Investigation on the properties and kinetics of glucose-fed aerobic granular sludge

Aerobic granulation is a process in which suspended biomass aggregate and form discrete well-defined granules in aerobic systems. To investigate the properties and kinetics of aerobic granular sludge, aerobic granules were cultivated with glucose synthetic wastewater in a series of sequencing batch reactors (SBR). The spherical shaped granules were observed on 8th day with the mean diameter of 0.1 mm. With the organic loading rate (OLR) being increased to 4.0 g COD L⁻¹ d⁻¹, aerobic granules grew matured with spherical shape. The size of granules ranged from 1.2 to 1.8 mm, and the corresponding settling velocity of individual granule was 24.2–36.4 m h⁻¹. The oxygen utilization rate (OUR) of mature granules was 41.90 g O₂ kg MLSS⁻¹ h⁻¹, which was two times higher than that of activated sludge (18.32 g O₂ kg MLSS⁻¹ h⁻¹). The experimental data indicated that the substrate utilization and biomass growth kinetics generally followed Monod's kinetics model. The corresponding kinetic coefficients of k (maximum specific substrate utilization rate), K_s (half velocity coefficient), Y (growth yield coefficient) and K_d (decay coefficient) were determined as follows, k_c = 23.65 d⁻¹, K_c = 3367.05 mg L⁻¹, K_N = 0.038 d⁻¹, K_N = 29.65 mg L⁻¹, Y = 0.1927–0.2022 mg MMLS (mg COD)⁻¹ and K_d = 0.00845–0.0135 d⁻¹, respectively. Those properties of aerobic granules made aerobic granules system had a short setup period, high substrate utilization rate and low sludge production.     

Dominance of yeast in activated sludge under acidic pH and high organic loading

Flow cytometry-fluorescent in situ hybridization (FC-FISH) was used to investigate the effect of controlled pH and/or varied organic loading on the content of yeast and bacterial cells in an activated sludge system (AS) individually operating in continuous and batch mode for treatment of high-strength industrial wastewater. Specifically, we attempted to develop a yeast-predominant activated sludge system (Y-AS). For the batch-mode AS, bacteria-dominated AS (B-AS) obtained at pH 6.5–7.5 induced higher chemical oxygen demand (COD) removal than Y-AS obtained at acidic pH (5.0–6.0 and 4.0–5.0). For the continuous-mode AS operating at COD loadings of 2.5–2.8 kg COD m⁻³ d⁻¹, it was difficult to achieve a Y-AS solely by controlling the pH level at 7.0 to 5.1 then to 4.1 because bacteria stably accounted for greater than 98% of the total cells, regardless of the pH levels. Therefore, the effects of varied COD loadings (2.1, 8.7 and 21.0 kg COD m⁻³ d⁻¹) on continuous-mode AS operation at acidic pH (4.5) was investigated. Both acidic pH and high COD loading levels were found to be prerequisites for yeast to dominate the sludge microbial community in the continuous-mode AS.     

Characteristics of simultaneous organic and nutrient removal in a pilot-scale vertical submerged membrane bioreactor (VSMBR) treating municipal wastewater at various temperatures

A pilot-scale vertical submerged membrane bioreactor (VSMBR) with anoxic and oxic zones in one reactor was operated in an attempt to reduce the problems concerning effective removal of organic matter and nutrients from municipal wastewater. Source water with total chemical oxygen demand (TCOD)/total nitrogen (TN) ratio of 5.5 was treated at various temperatures (13–25 °C) over an interval of about 1 year. As a result, total suspended solid (TSS) and TCOD were removed by 100% and higher than 98%, respectively. Moreover, the average removal efficiencies of TN and total phosphorus (TP) were found to be 74% and 78% at 8 h-hydraulic retention time (HRT) and 60-days sludge retention time (SRT). Under these conditions, the specific removal rates (SRR) of TN and TP were found to be 0.093 kg N m⁻³ day⁻¹ and 0.008 kg P m⁻³ day⁻¹, and the daily production of excess sludge (DPES), 0.058 kg TSS day⁻¹.     

Dynamics of the microfauna community in a full-scale municipal wastewater treatment plant experiencing sludge bulking

We investigated the dynamics of the microfauna community in activated sludge, with special reference to sludge bulking, in two parallel municipal wastewater treatment systems in Beijing, China over a period of 14 months. Annual cyclic changes in microfauna community structures occurred in both systems. RELATE analysis based on Spearman's Rank correlation indicated that microfauna community structures were highly correlated with the sludge volume index (SVI) (p < 0.001), which indicates sludge settleability. Nutrient conditions of raw sewage (p < 0.01) and hydraulic retention time (HRT) (p < 0.05) were also related to microfauna community structures. Abundances of the species Epistylis plicatilis and Vorticella striata increased significantly with an increase in SVI (p < 0.001) and decrease in water temperature (p < 0.001), suggesting that sludge bulking may have created favorable conditions for the two species, even under unfavorable temperature conditions. Sludge de-flocculation primarily due to the excessive growth of Microthrix parvicella-like filaments could be an important driving force for the microfauna community changes. The release of flocculated non-filamentous bacteria may represent a suitable food source for these species. The two species may be considered as potential bioindicators for sludge bulking.     

Anaerobic thermophilic digestion of cutting oil wastewater: Effect of co-substrate

This paper describes the thermophilic (55 °C) anaerobic biodegradation of a mixed feed composed of vinasses and cutting oil wastewater (COW) in a laboratory upflow anaerobic fixed-film reactor (UAFF) with a porous support medium. The experimental protocol was defined to examine the effect of increasing the percentage of cutting oil wastewater in the feed.The UAFF reactor was initially started-up with vinasses as the only carbon source at an organic loading rate of 22.3 kg COD/m³ day and HRT of 0.8 days using porous particles as the support (SIRAN). The percentage of organic matter composed of vinasses was subsequently reduced while increasing the amount of cutting oil until 100% of cutting oil wastewater was added in the feed. Four stages were considered in the study (0, 42.4, 66.6 and 100% COW). HRT was adjusted in order to maintain an approximately constant organic loading rate applied to the system. Under theses conditions, the UAFF reactor was subjected to a programme of steady-state operation with hydraulic retention times (HRT) in the range 0.8–0.15 days and organic loading rates (OLR) between 22.3 and 14.9 kg COD/m³ day in order to evaluate the treatment capacity of the system.The COD removal efficiency was found to be 87% COD and 94.6% TOC in the reactor when treating vinasses at 22.3 kg COD/m³ day. The volumetric methane level produced in the digester reached 0.45 m³/m³ day. After an operating period of 120 days, the reactor was fed with cutting oil wastewater (COW) as the only source of carbon. An OLR of 16.7 kg COD/m³ day was achieved with 85.8% COD removal efficiency (58.1%TOC) in the experimental UAFF reactor. Under these conditions the volumetric methane produced in the digester was negligible.Hence, COW can be removed, if not degraded, by anaerobic treatment in the presence of a biodegradable co-substrate. Wine vinasses degradation creates conditions for non-biological removal of COW constituents. More studies are necessary in order to test the mechanisms of organic removal when biodegradation apparently had ceased. Also, toxicity assays of COW are necessary to evaluate the toxicity to the methanogenic community.     

Application of polyethylene glycol immobilized Clostridium sp. LS2 for continuous hydrogen production from palm oil mill effluent in upflow anaerobic sludge blanket reactor

A novel polyethylene glycol (PEG) gel was fabricated and used as a carrier to immobilize Clostridium sp. LS2 for continuous hydrogen production in an upflow anaerobic sludge blanket (UASB) reactor. Palm oil mill effluent (POME) was used as the substrate carbon source. The optimal amount of PEG-immobilized cells for anaerobic hydrogen production was 12% (w/v) in the UASB reactor. The UASB reactor containing immobilized cells was operated at varying hydraulic retention times (HRT) that ranged from 24 to 6 h at 3.3 g chemical oxygen demand (COD)/L/h organic loading rate (OLR), or at OLRs that ranged from 1.6 to 6.6 at 12 h HRT. The best volumetric hydrogen production rate of 336 mL H₂/L/h (or 15.0 mmol/L/h) with a hydrogen yield of 0.35 L H₂/g COD_removed was obtained at a HRT of 12 h and an OLR of 5.0 g COD/L/h. The average hydrogen content of biogas and COD reduction were 52% and 62%, respectively. The major soluble metabolites during hydrogen fermentation were butyric acid followed by acetic acid. It is concluded that the PEG-immobilized cell system developed in this work has great potential for continuous hydrogen production from real wastewater (POME) using the UASB reactor.     

Recycling of agro-industrial sludge through vermitechnology

This work illustrates the feasibility of vermitechnology to stabilize sludge from an agro-industry. To achieve the goal, industrial sludge (IS) was mixed with three different bulky agents, i.e. cow dung (CD), biogas plant slurry (BGS) and wheat straw (WS), in different ratios to produce nine different feed mixtures for earthworm Eisenia fetida. Vermicomposting bedding material was analyzed for its different physic-chemical parameters after 15 weeks of experimentations. In all waste mixtures, a decrease in pH, organic C and C:N ratio, but increase in total N, available P, exchangeable K, exchangeable Ca and trace elements (Mg, Fe and Zn) was recorded. IS (40%) + CD (60%) and IS (40%) + BGS (60%) vermibeds showed the highest mineralization rate and earthworm growth patterns during vermicomposting process. Vermicompost contains (dry weight basis) a considerable range of plant available forms of P (17.5–28.9 g kg^?1), K (13.8–21.4 g kg^?1), Ca (41.1–63.4 g kg^?1), Mg (262.4–348.3 mg kg^?1), Fe (559.8–513.0 mg kg^?1) and Zn (363.1–253.6 mg kg^?1). Earthworm growth parameters, i.e. biomass gain, total cocoon production, individual growth rate (mg wt. worm^?1 day^?1), natality rate, total fecundity were optimum in bedding containing 20–40% industrial sludge. C:N ratio of worm-processed material was within the agronomic acceptable or favorable limit (<15–20). The results clearly suggested that vermitechnology can be a potential technology to convert industrial sludges into vermifertilizer for sustainable land restoration practices.     

Effect of sulfate and iron on physico-chemical characteristics of anaerobic granular sludge

This research investigated the effect of the substrate composition (no substrate, glucose, glucose + sulfate or glucose + sulfate + iron) on the physico-chemical characteristics of two different anaerobic granular sludges as a function of time. The sludges were fed batch wise (pH 7, 30 °C) at an organic loading rate of 1.2 g COD l⁻¹ d⁻¹ (0.04 g COD g VSS⁻¹ day⁻¹) for 30 days. The presence of sulfate (COD/sulfate ratio = 1) in the feed of glucose fed anaerobic sludges did not change the physico-chemical characteristics throughout the incubation. In contrast, the presence of iron in the feed (in addition to glucose and sulfate, COD/iron ratio = 1) reduced the protein and carbohydrate content in the SMP and EPS with about 50% after 30 days incubation compared to the other feeding conditions. The sludge grown on glucose + sulfate + iron contained much more iron (+300–500%) and sulfur (+200–350%) than the other incubated sludges both after 14 and 30 days. The higher mineral content (lower VSS content) and the decrease of the EPS content contributed to the disintegration of iron fed granules, as shown by their lower size particles. However, the iron fed sludge displayed a higher granule strength than the other incubated sludges. Although an appreciable variation in the granule strength was noticed between the sludges investigated, it was not possible to relate these differences to their inorganic composition, the chemical composition of the extracted polymers or to the physical characteristics investigated.     

Removal of carbon and nutrients from low strength domestic wastewater by expanded granular sludge bed-zeolite bed filtration (EGSB-ZBF) integrated treatment concept

The performance of an expanded granular sludge bed (EGSB) reactor coupled with zeolite bed filtration (ZBF) for treating low strength domestic wastewater was monitored at 35 °C for 7 months. The whole operation period of EGSB system was divided into five phases. Each phase ran at up-flow velocity (m/h) of 0.51, 1.02, 3.57, 2.05, 9.69, and hydraulic retention time (HRT) (h) of 6, 3, 0.87, 1.5, 0.32, respectively. The influent chemical oxygen demand (COD) was kept approximate at 150 ± 100 mg/L. Under these conditions, the COD removal efficiency of using EGSB system in five phases reached to 81.08, 57.94, 82.79, 56.58 and 79.52%, respectively. Moreover, since nutrients such as NH₄⁺ and PO₄³⁻ were only removed to a limited extent by EGSB, additional treatment is required. The ZBF was employed in phase 2 as a post-treatment following EGSB. NH₄⁺ and PO₄³⁻ concentrations were decreased by 100%, respectively, in the first 2 or 3 d using fresh zeolite. The simple design and excellent treatment performance indicated that this system could be used as a novel Sewage Integrated Treatment System (SITS) for developing country especially in a tropical area.     

Sewage treatment in a combined up-flow anaerobic sludge blanket (UASB)–down-flow hanging sponge (DHS) system

The performance of up-flow anaerobic sludge blanket (UASB) in combination with down-flow hanging sponge (DHS) system for sewage treatment at an average wastewater temperature of 15 °C has been investigated for 6 months. The results showed that a combined system operated at a total HRT of 10.7 h and total SRT of 88 days represents a cost effective sewage treatment process. The average COD_total and BOD_5 total concentrations measured in the final effluent of the total system (UASB + DHS) amounted to 43 and 3.0 mg/l, respectively, corresponding to the overall removal efficiency of 90% for COD_total and 98% for BOD_5 total. The total process provided a final effluent containing a low concentration of 12 mg/l for TSS.Eighty-six percent of ammonia was eliminated at space loading rate of 1.6 kg COD/m³ d and HRT of 2.7 h. The calculated nitrification rate of the DHS system according to the nitrate and nitrite production amounted to 0.18 kg/m³ d. The removal of F. coliform in the UASB reactor only amounted to 0.86 log₁₀. On the other hand, the F. coliform concentration dropped substantially, i.e. by 2.6 log₁₀ in the DHS system resulting only 2.7 × 10³/100 ml in the final effluent.The calculated average sludge production for UASB operated at an HRT of 8.0 h amounted to 30 g TSS/d, corresponding to sludge yield coefficient of 0.2 g TSS/g total COD removed, while it was indeed very low only 6.0 g TSS/d corresponding to sludge yield coefficient of 0.09 g TSS/g total COD removed, for DHS system.The DHS profile results revealed that in the first and second segment of DHS system, the COD_total, BOD_5 total and TSS was eliminated, followed by the oxidation of ammonia in the next segments.     

Dairy wastewater polluting load and treatment performances of an industrial three-cascade-reactor plant

An industrial three-cascade-reactor plant treating 45 m³ d^?1 of dairy wastewater (DW) was monitored for approx. one year to investigate the effect of variable daily influent loads. It removed more than 85% COD, NH₄-N and non-ionic and anionic surfactants from DW within the loads 7–24, 0.4–2.3, 0.4–0.7 and 0.1–0.5 kg d^?1, respectively; NH₄-N removal, in particular, was almost quantitative. Although the degradation of the above parameters below the lower load thresholds declined to 78.7, 87.5, 50.2 and 64.7%, respectively, their residual concentrations met effluent discharge standards. The biomass settling properties, assessed as sludge volume index (SVI), were satisfactory (generally lower than 150 ml g^?1) regardless of the organic load of the influent. The depletion of the pollutant load took mainly place in the first reactor albeit a significant contribution to the removal of the slowly degradable organic matter fraction was given by the two subsequent reactors.     

Response of native grasses and Cicer arietinum to soil polluted with mining wastes: Implications for the management of land adjacent to mine sites

Mine tailings are an environmental problem in Southern Spain because wind and water erosion of bare surfaces results in the dispersal of toxic metals over nearby urban or agricultural areas. Revegetation with tolerant native species may reduce this risk. We grew two grasses, Lygeum spartum and Piptatherum miliaceum, and the crop species Cicer arietinum (chickpea) under controlled conditions in pots containing a mine tailings mixed into non-polluted soil to give treatments of 0%, 25%, 50%, 75% and 100% mine tailings. We tested a neutral (pH 7.4) mine tailings which contained high concentrations of Cd, Cu, Pb and Zn. Water-extractable metal concentrations increased in proportion to the amount of tailings added. The biomass of the two grasses decreased in proportion to the rate of neutral mine-tailing addition, while the biomass of C. arietinum only decreased in relation to the control treatment. Neutron radiography revealed that root development of C. arietinum was perturbed in soil amended with the neutral tailings compared to those of the control treatment, despite a lack of toxicity symptoms in the shoots. In all treatments and for all metals, the plants accumulated higher concentrations in the roots than in shoots. The highest concentrations occurred in the roots of P. miliaceum (2500 mg kg^?1 Pb, 146 mg kg^?1 Cd, 185 mg kg^?1 Cu, 2700 mg kg^?1 Zn). C. arietinum seeds had normal concentrations of Zn (70–90 mg kg^?1) and Cu (6–9 mg kg^?1). However, the Cd concentration in this species was ～1 mg kg^?1 in the seeds and 14.5 mg kg^?1 in shoots. Consumption of these plant species by cattle and wild fauna may present a risk of toxic metals entering the food chain.     

Optimal dimethyl sulfoxide biodegradation using activated sludge from a chemical plant

Inappropriate biological treatment of dimethyl sulfoxide (DMSO) used by opto-electronics and semi-conductor industries would result in production of malodorous compounds, e.g. dimethyl sulfide, methane-thiol and hydrogen sulfide. The best sludge for DMSO biodegradation was obtained from the activated sludge of a chemical company that used to provide DMSO for the above industries. Under the optimal conditions of pH 7.0–8.5 and 30 °C, the highest removal efficiency in treatment of 500 mg l⁻¹ of DMSO occurred at the rate of 0.078 g DMSO per gram suspended solids per day corresponding to 37 h for complete DMSO biodegradation in a shake-flask culture. However, the time needed for DMSO biodegradation could be reduced to 16 h at the rate of 0.153 g DMSO per gram suspended solids per day if a repeated-batch mode was adopted, indicating that an acclimation period is required by the DMSO degraders. The reaction time could further be shortened to less than 10 h with 95% removal of the 750 mg l⁻¹ DMSO at the maximum rate of 0.909 g DMSO per gram suspended solids per day using an oxygen-enriched air-lift bioreactor. No malodorous compounds, such as dimethyl sulfide, were produced revealing that the biodegradation pathway is oxidative and can solve the odor problems common in the biological wastewater treatment plant of the abovementioned industries.