Continuous treatment of the organic fraction of municipal solid waste in an anaerobic two-stage membrane process with liquid recycle

The stability and performance of a two-stage anaerobic membrane process was investigated at different organic loading rates (OLRs) and Hydraulic Retention Times (HRTs) over 200 days. The Hydrolytic Reactor (HR) was fed with the Organic Fraction of Municipal Solid Waste (OFMSW), while the leachate from the HR was fed continuously to two Submerged Anaerobic Membrane Bioreactors (SAMBR1 and 2). The Total COD (TCOD) of the leachate varied over a wide range, typically between 4000 and 26,000 mg/L while the Soluble COD (SCOD) in the permeate was in the range 400-600 mg/L, achieving a COD removal greater than 90% at a HRT of 1.6-2.3 days in SAMBR1. The operation was not sustainable below this HRT due to a membrane flux limitation at 0.5-0.8 L/m² h (LMH), which was linked to the increasing MLTSS. SCOD in the recycled permeate did not build up indicating a slow degradation of recalcitrants over time. SAMBR2 was run in parallel with SAMBR1 but its permeate was treated aerobically in an Aerobic Membrane Bioreactor (AMBR). The AMBR acted as a COD-polishing and ammonia removal step. About 26% of the recalcitrant SCOD from SAMBR2 could be aerobically degraded in the AMBR. In addition, 97.7 % of the ammonia-nitrogen was converted to nitrate in the AMBR at a maximum nitrogen-loading rate of 0.18 kg NH₄⁺-N/m³ day. GC-MS analysis was performed on the reactor effluents to determine their composition and what compounds were recalcitrant.     

The sensitivity of fixed-bed biological perchlorate removal to changes in operating conditions and water quality characteristics

Flow rate, electron donor addition, and biomass control were evaluated in order to optimize perchlorate (ClO₄⁻) removal from drinking water using biologically active carbon (BAC) filtration. Influent dissolved oxygen (DO) was lowered from ambient conditions to approximately 2.5 mg/L for all experiments using a nitrogen sparge. When influent nitrate concentration was 0-2.0 mg/L, 1.6-2.8 mg/L as carbon of acetate or ethanol was required to achieve and sustain the complete removal of 50 μg/L perchlorate in a BAC filter. Most or all of the exogenous acetate and ethanol was removed during biofiltration. When a 72-h electron donor feed failure was simulated, a maximum perchlorate breakthrough of 18 μg/L was observed and, once electron donor was reapplied, 9 days were required to reestablish complete perchlorate removal. During a 24-h electron donor feed failure simulation, the maximum effluent perchlorate concentration detected was 6.7 μg/L. Within 24 h of reactivating the electron donor, the filter regained its capacity to consistently remove 50 μg/L perchlorate to below detection. Although biomass growth diminished the filter's ability to consistently remove perchlorate, a cleaning procedure immediately restored stable, complete perchlorate removal. This cleaning procedure was required approximately every 50 days (4800 bed volumes) when influent DO concentration was 2.5 mg/L. Empty-bed contact time (EBCT) experiments showed that 80% perchlorate removal was achieved using a 5-min EBCT, and complete perchlorate removal was observed for an EBCT of 9 min. It was also demonstrated that BAC filtration consistently removed perchlorate to below detection for influent perchlorate concentrations ranging from 10 to 300 μg/L, influent sulfate concentrations between 0 and 220 mg/L, influent pH values of 6.5-9.0, and operating temperatures of 5-22°C.     

Trace metal concentrations in the North-western Mediterranean atmospheric aerosol between 1986 and 2008: Seasonal patterns and decadal trends

Climatic and anthropogenic changes are able to engender modifications in the aerosol composition at different geographical and temporal scales. The present study addresses this question for the trace metal concentrations (TM = Al, Fe, Mn, Co, Ni, Cu, Pb, Cd and Zn) of aerosol from the North-western Mediterranean coast of France (Cap Ferrat, nearby Nice) between 1986 and 2008. From seasonal variations (2006-08) and decadal trends (1986-2008) of TM concentrations, three groups of elements can be distinguished. They consist of different aerosol sources: crustal-derived elements (Al, Fe, Mn and Co), trace metals of anthropogenic origin (Pb, Cd and Zn) and a third, intermediate, group of trace metals that presented both anthropogenic and natural/crustal influences (Ni and Cu). Reproducible seasonal patterns were observed for crustal and intermediate elements with highest concentrations between May and November, while anthropogenic trace metals did not show a pronounced seasonal cycle. Nevertheless, highest concentrations of anthropogenic trace metals occurred mostly in autumn/winter. Aerosol concentrations of anthropogenic TMs decreased remarkably over the last two decades, while crustal trace metals did not show any evolution. Nickel and copper aerosol concentrations remained constant, as well. Lead concentrations decreased from 1986 (29.34 ng m^− 3) to 2008 (3.33 ng m^− 3), overall by 90%. Cadmium and zinc aerosol concentrations decreased by 66 and 54%, respectively, between 1998 and 2006-08, from 0.27 to 0.09 ng m^− 3 and from 23.9 to 10.9 ng m^− 3, respectively. These findings demonstrate the response of the atmospheric environment to the implementation of antipollution policies. Possible changes of trace metal emissions sources and local influences are discussed.     

Effect of pH, ionic strength, dissolved organic carbon, time, and particle size on metals release from mine drainage impacted streambed sediments

Acid-mine drainage (AMD) input to a stream typically results in the stream having a reduced pH, increased concentrations of metals and salts, and decreased biological productivity. Removal and/or treatment of these AMD sources is desired to return the impacted stream(s) to initial conditions, or at least to conditions suitable for restoration of the aquatic ecosystem. Some expected changes in the water chemistry of the stream following removal of AMD input include an increase in pH, a decrease in ionic strength, and an increase in dissolved organic carbon (DOC) concentrations from increased biological activity in the absence of toxic metals concentrations. These changes in water chemistry may cause the existing contaminated bed sediments to become a source of metals to the stream water. Streambed sediments, collected from North Fork Clear Creek (NFCC), Colorado, currently impacted by AMD, were assessed for the effects of pH, ionic strength, DOC concentration, time, and particle size on metals release using a factorial design. The design included two levels for each chemical parameter (ionic strength = 40 and 80% lower than ambient; pH = 6 and 8; and DOC = 1 and 3 mg/l higher than ambient), ten sampling times (from zero to 48 h), and two size fractions of sediments (63 μm ≤ x < 2 mm and <63 μm). Greater concentrations of metals were released from the smaller sized sediments compared with the larger, with the exception of Cu. A mild acid digestion (0.6 M HCl) evaluated the amount of each metal that could be removed easily from each of the sediment size fractions. Release of all metals over all time points, treatments, and from both sediment sizes was less than 1% of the extractable concentrations, with the exception of Mn, which ranged from 4 to 7% from the smaller sized sediment. Greater percentages of the 0.6 M HCl-extractable concentrations of Cu, Fe, and Zn were released from the larger sized sediment, while this was true for release of Cd and Mn from the smaller sized sediment. Thus, at least for Cd and Mn, the observed higher concentrations released from the smaller sized sediment with each treatment solution is not simply a function of these particles having higher concentrations available for release, but that these metals also are more readily released from the smaller sediment particles versus the larger. DOC concentration strongly influenced the release of Cu; ionic strength strongly influenced the release of Cd, Mn, and Zn; and interaction effects were observed with the release of Cu, Mn, and Zn from the larger size fraction and with the release of Zn from the smaller size fraction. Overall, results suggest that the expected changes in water chemistry following removal/treatment of the AMD sources would result in a release of metals from the existing sediments, with a greater effect on the release of Cu and Fe, than on the release of Cd, Mn, and Zn.     

Effect of air-assisted backwashing on the performance of an anaerobic fixed-bed bioreactor that simultaneously removes nitrate and arsenic from drinking water sources

Contaminant removal from drinking water sources under reducing conditions conducive for the growth of denitrifying, arsenate reducing, and sulfate reducing microbes using a fixed-bed bioreactor may require oxygen-free gas (e.g., N₂ gas) during backwashing. However, the use of air-assisted backwashing has practical advantages, including simpler operation, improved safety, and lower cost. A study was conducted to evaluate whether replacing N₂ gas with air during backwashing would impact performance in a nitrate and arsenic removing anaerobic bioreactor system that consisted of two biologically active carbon reactors in series. Gas-assisted backwashing, comprised of 2 min of gas injection to fluidize the bed and dislodge biomass and solid phase products, was performed in the first reactor (reactor A) every two days. The second reactor (reactor B) was subjected to N₂ gas-assisted backwashing every 3-4 months. Complete removal of 50 mg/L NO₃⁻ was achieved in reactor A before and after the switch from N₂-assisted backwashing (NAB) to air-assisted backwashing (AAB). Substantial sulfate removal was achieved with both backwashing strategies. Prolonged practice of AAB (more than two months), however, diminished sulfate reduction in reactor B somewhat. Arsenic removal in reactor A was impacted slightly by long-term use of AAB, but arsenic removals achieved by the entire system during NAB and AAB periods were not significantly different (p > 0.05) and arsenic concentrations were reduced from approximately 200 μg/L to below 20 μg/L. These results indicate that AAB can be implemented in anaerobic nitrate and arsenic removal systems.     

Effects of altered groundwater chemistry upon the pH-dependency and magnitude of bacterial attachment during transport within an organically contaminated sandy aquifer

The effects of a dilute (ionic strength = 5 × 10⁻³ M) plume of treated sewage, with elevated levels (3.9 mg/L) of dissolved organic carbon (DOC), upon the pH-dependency and magnitude of bacterial transport through an iron-laden, quartz sand aquifer (Cape Cod, MA) were evaluated using sets of replicate, static minicolumns. Compared with uncontaminated groundwater, the plume chemistry diminished bacterial attachment under mildly acidic (pH 5.0-6.5) in-situ conditions, in spite of the 5-fold increase in ionic strength and substantively enhanced attachment under more alkaline conditions. The effects of the hydrophobic neutral and total fractions of the plume DOC; modest concentrations of fulvic and humic acids (1.5 mg/L); linear alkyl benzene sulfonate (LAS) (25 mg/L); Imbentin (200 μg/L), a model nonionic surfactant; sulfate (28 mg/L); and calcium (20 mg/L) varied sharply in response to relatively small changes in pH, although the plume constituents collectively decreased the pH-dependency of bacterial attachment. LAS and other hydrophobic neutrals (collectively representing only ∼3% of the plume DOC) had a disproportionately large effect upon bacterial attachment, as did the elevated concentrations of sulfate within the plume. The findings further suggest that the roles of organic plume constituents in transport or bacteria through acidic aquifer sediments can be very different than would be predicted from column studies performed at circumneutral pH and that the inorganic constituents within the plume cannot be ignored.     

An evaluation of the reactivity of synthetic and natural apatites in the presence of aqueous metals

Metal removal from contaminated effluents was examined following reaction with natural apatites of biological and geological origin or a synthetic hydroxylapatite (HAP). Mammalian meat and bone meal (MBM), a by-product from meat industry, was the biological apatite source. The effect of incineration on metal removal capacity of MBM and HAP was also examined. The reactivity of apatites for all tested metals (Pb, Cd, Cu and Zn) followed the general order: synthetic > biological > mineral. For all apatites tested, Pb was removed best and preferentially from multi-metal solutions. MBM and HAP (0.5 g solid) removed Pb completely from both highly concentrated single metal solutions (50 ml, 1000 mg/L Pb) and from multi-metal solutions (50 ml) with 100 mg/L each of Cd, Cu and Zn in addition to Pb. The incineration of MBM (725 °C and 850 °C) reduced significantly its capacity for removal of Zn (by 47%, from 56 mg/g to 9 mg/g) and Cd (by 38%, from 53 mg/g to 13 mg/g) in particular and to a lesser extent for Cu (by 14%, from 61 mg/g to 46 mg/g) while the removal of Pb was not affected (100 mg/g). The same pattern was observed for incinerated HAP. SEM and XRD analysis indicated that HAP reacted with the metals by precipitation of pure metal phosphates—Pb hydroxylapatite, Zn phosphate (hopeite), a Cd phosphate (identified only by ED-SEM) and Cu phosphate (libenthenite).     

Nitrogen and phosphorus removal from municipal wastewater effluent using microalgal biofilms

Microalgal biofilms have so far received little attention as post-treatment for municipal wastewater treatment plants, with the result that the removal capacity of microalgal biofilms in post-treatment systems is unknown. This study investigates the capacity of microalgal biofilms as a post-treatment step for the effluent of municipal wastewater treatment plants. Microalgal biofilms were grown in flow cells with different nutrient loads under continuous lighting of 230 μmol/m²/s (PAR photons, 400-700 nm). It was found that the maximum uptake capacity of the microalgal biofilm was reached at loading rates of 1.0 g/m²/day nitrogen and 0.13 g/m²/day phosphorus. These maximum uptake capacities were the highest loads at which the target effluent values of 2.2 mg/L nitrogen and 0.15 mg/L phosphorus were still achieved. Microalgal biomass analysis revealed an increasing nitrogen and phosphorus content with increasing loading rates until the maximum uptake capacities. The internal nitrogen to phosphorus ratio decreased from 23:1 to 11:1 when increasing the loading rate. This combination of findings demonstrates that microalgal biofilms can be used for removing both nitrogen and phosphorus from municipal wastewater effluent.     

Biotreatment and bioassessment of heavy metal removal by sulphate reducing bacteria in fixed bed reactors

In this work a batch-optimised mixture (w/w %: 6% leaves, 9% compost, 3% Fe(0), 30% silica sand, 30% perlite, 22% limestone) was investigated in a continuous fixed bed column reactor for the treatment of synthetic acid-mine drainage (AMD). A column reactor was inoculated with sulphate-reducing bacteria and fed with a solution containing sulphate and heavy metals (As(V), Cd, Cr(VI), Cu and Zn). At steady state, sulphate abatement was 50 ± 10%, while metals were totally removed. A degradation rate constant (k) of 0.015 ± 0.001 h⁻¹ for sulphate removal was determined from column data by assuming a first order degradation rate. Reduction of AMD toxicity was assessed by using the nematode Caenorhabditis elegans as a test organism. A lethality assay was performed with the toxicants before and after the treatment, showing that only 5% of the animals were still alive after 48 h in presence of the contaminants, while the percentage increased to 73% when the nematodes were exposed to the solution eluted from the column.     

Heavy metals: confounding factors in the response of New Zealand freshwater fish assemblages to natural and anthropogenic acidity

Acidification of freshwaters is a global phenomenon, occurring both through natural leaching of organic acids and through human activities from industrial emissions and mining. The West Coast of the South Island, New Zealand, has both naturally acidic and acid mine drainage (AMD) streams enabling us to investigate the response of fish communities to a gradient of acidity in the presence and absence of additional stressors such as elevated concentrations of heavy metals. We surveyed a total of 42 streams ranging from highly acidic (pH 3.1) and high in heavy metals (10 mg L⁻¹ Fe; 38 mg L⁻¹ Al) to circum-neutral (pH 8.1) and low in metals (0.02 mg L⁻¹ Fe; 0.05 mg L⁻¹ Al). Marked differences in pH and metal tolerances were observed among the 15 species that we recorded. Five Galaxias species, Anguilla dieffenbachii and Anguillaaustralis were found in more acidic waters (pH< 5), while bluegill bullies (Gobiomorphus hubbsi) and torrentfish (Cheimarrichthys fosteri) were least tolerant of low pH (minimum pH 6.2 and 5.5, respectively). Surprisingly, the strongest physicochemical predictor of fish diversity, density and biomass was dissolved metal concentrations (Fe, Al, Zn, Mn and Ni) rather than pH. No fish were detected in streams with dissolved metal concentrations > 2.7 mg L⁻¹ and nine taxa were only found in streams with metal concentrations < 1 mg L⁻¹. The importance of heavy metals as critical drivers of fish communities has not been previously reported in New Zealand, although the mechanism of the metal effects warrants further study. Our findings indicate that any remediation of AMD streams which seeks to enable fish recolonisation should aim to improve water quality by raising pH above ≈ 4.5 and reducing concentrations of dissolved Al and Fe to < 1.0 mg L⁻¹.     

Aerobic degradation of sulfanilic acid using activated sludge

This paper evaluates the aerobic degradation of sulfanilic acid (SA) by an acclimatized activated sludge. The sludge was enriched for over three months with SA (>500 mg/L) as the sole carbon and energy source and dissolved oxygen (DO, >5 mg/L) as the primary electron acceptor. Effects of aeration rate (0-1.74 L/min), DO concentration (0-7 mg/L) and initial SA concentration (104-1085 mg/L) on SA biodegradation were quantified. A modified Haldane substrate inhibition model was used to obtain kinetic parameters of SA biodegradation and oxygen uptake rate (OUR). Positive linear correlations were obtained between OUR and SA degradation rate (R² ≥ 0.91). Over time, the culture consumed more oxygen per SA degraded, signifying a gradual improvement in SA mineralization (mass ratio of O₂: SA at day 30, 60 and 120 were 0.44, 0.51 and 0.78, respectively). The concomitant release of near stoichiometric quantity of sulphate (3.2 mmol SO₄²⁻ released from 3.3 mmol SA) and the high chemical oxygen demand (COD) removal efficacy (97.1%) indicated that the enriched microbial consortia could drive the overall SA oxidation close to a complete mineralization. In contrast to other pure-culture systems, the ammonium released from the SA oxidation was predominately converted into nitrate, revealing the presence of ammonium-oxidizing bacteria (AOB) in the mixed culture. No apparent inhibitory effect of SA on the nitrification was noted. This work also indicates that aerobic SA biodegradation could be monitored by real-time DO measurement.     

Health risk from heavy metals via consumption of food crops in the vicinity of Dabaoshan mine, South China

Heavy metal contamination of soils resulting from mining and smelting is causing major concern due to the potential risk involved. This study was designed to investigate the heavy metal (Cu, Zn, Pb and Cd) concentrations in soils and food crops and estimate the potential health risks of metals to humans via consumption of polluted food crops grown at four villages around the Dabaoshan mine, South China. The heavy metal concentrations in paddy and garden soils exceeded the maximum allowable concentrations for Chinese agricultural soil. The paddy soil at Fandong village was heavily contaminated with Cu (703 mg kg^− 1), Zn (1100 mg kg^− 1), Pb (386 mg kg^− 1) and Cd (5.5 mg kg^− 1). Rice tended to accumulated higher Cd and Pb concentration in grain parts. The concentrations of Cd, Pb and Zn in vegetables exceeded the maximum permissible concentration in China. Taro grown at the four sampled villages accumulated high concentrations of Zn, Pb and Cd. Bio-accumulation factors for heavy metals in different vegetables showed a trend in the order: Cd > Zn > Cu > Pb. Bio-accumulation factors of heavy metals were significantly higher for leafy than for non-leafy vegetable. The target hazard quotient (THQ) of rice at four sites varied from 0.66-0.89 for Cu, 0.48-0.60 for Zn, 1.43-1.99 for Pb, and 2.61-6.25 for Cd. Estimated daily intake (EDI) and THQs for Cd and Pb of rice and vegetables exceeded the FAO/WHO permissible limit. Heavy metal contamination of food crops grown around the mine posed a great health risk to the local population through consumption of rice and vegetables.     

Interaction between temperature and ammonia in mesophilic digesters for animal waste treatment

Four anaerobic sequencing batch reactors (ASBRs) were operated during a period of 988 days to evaluate the effect of temperature, ammonia, and their interconnectivity on the methane yield of anaerobic processes for animal waste treatment. During period 1 (day 0-378), the methane yield was 0.31 L CH₄/g volatile solids (VS) for all digesters (with no statistical differences among them) at a temperature and total ammonium-N levels of 25 °C and ∼1200 mg NH₄⁺-N/L, respectively. During period 2 (day 379-745), the methane yield at 25 °C decreased by 45% when total ammonium-N and ammonia-N were increased in two of the four ASBRs to levels >4000 mg NH₄⁺-N/L and >80 mg NH₃-N/L, respectively. During period 3 (day 746-988), this relative inhibition was reduced from 45% to 13% compared to the low-ammonia control reactors when the operating temperature was increased from 25 °C to 35 °C (while the free ammonia levels increased from ∼100 to ∼250 mg NH₃-N/L). The 10 °C increase in temperature doubled the rate constant for methanogenesis, which overwhelmed the elevated toxicity effects caused by the increasing concentration of free ammonia. Thus, the farmer/operator may alleviate ammonia toxicity by increasing the operating temperature within the mesophilic range. We extrapolated our data to correlate temperature, ammonia, and methane yield and to hypothesize that the difference between high- and low-ammonia reactors is negligible at the optimum mesophilic temperature of 38 °C.     

Multiple site study of recent atmospheric metal (Pb, Zn and Cu) deposition in the NW Iberian Peninsula using peat cores

In order to estimate atmospheric metal deposition in Southern Europe since the beginning of the Industrial Period (~ 1850 AD), concentration profiles of Pb, Zn and Cu were determined in four ²¹⁰Pb-dated peat cores from ombrotrophic bogs in Serra do Xistral (Galicia, NW Iberian Peninsula). Maximum metal concentrations varied by a factor of 1.8 for Pb and Zn (70 to 128 μg g⁻¹ and 128 to 231 μg g⁻¹, respectively) and 3.5 for Cu (11 to 37 μg g⁻¹). The cumulative metal inventories of each core varied by a factor of 3 for all analysed metals (132 to 329 μg cm⁻² for Pb, 198 to 625 μg cm⁻² for Zn and 22 to 69 μg cm⁻² for Cu), suggesting differences in net accumulation rates among peatlands. Although results suggest that mean deposition rates vary within the studied area, the enhanced ²¹⁰Pb accumulation and the interpretation of the inventory ratios (²¹⁰Pb/Pb, Zn/Pb and Cu/Pb) in two bogs indicated that either a record perturbation or post-depositional redistribution effects must be considered. After correction, Pb, Zn and Cu profiles showed increasing concentrations and atmospheric fluxes since the mid-XX^th century to maximum values in the second half of the XX^th century. For Pb, maximum fluxes were observed in 1955-1962 and ranged from 16 to 22 mg m⁻² yr⁻¹ (mean of 18 ± 1 mg m⁻² yr⁻¹), two orders of magnitude higher than in the pre-industrial period. Peaks in Pb fluxes in Serra do Xistral before the period of maximum consumption of leaded petrol in Europe (1970s-1980s) suggest the dominance of local pollutant sources in the area (i.e. coal mining and burning). More recent peaks were observed for Zn and Cu, with fluxes ranging from 32 to 52 mg m⁻² yr⁻¹ in 1989-1996, and from 4 to 9 mg m⁻² yr⁻¹ in 1994-2001, respectively. Our results underline the importance of multi-core studies to assess both the integrity and reliability of peat records, and the degree of homogeneity in bog accumulation. We show the usefulness of using the excess ²¹⁰Pb inventory to distinguish between differential metal deposition, accumulation or anomalous peat records.     

Water management — A tool for methane mitigation from irrigated paddy fields

Water drainage is considered to be one of the important practices that reduce the CH₄ efflux from paddy fields. In this study, four different drainage systems (continuous flooding, tillering stage drainage, mid-season drainage and multiple drainage) were compared to find out the best one, for attenuation of CH₄ emission from rice fields. Except for continuous flooding, from all the other three drainage systems, irrigation water from the paddy fields was drained out at the different stages of the crop cycle. Highest efflux of the methane was recorded from continuously flooded plots (346.6 mg/m²/day), followed by 9% less CH₄ efflux from tillering stage drainage (315.1 mg/m²/day), 36.7% less efflux from mid-season drainage (219.3 mg/m²/day) and the least 41% CH₄ efflux from multiple drainage plots (204.7 mg/m²/day). Among all the four different drainage systems applied, mid-season drainage and multiple drainage were found to be highly effective in mitigating methane efflux. Redox potential of the soil of the drainage system was found to be inversely proportional to the methane efflux from all the treatments.     

Wetland treatment at extremes of pH: a review

Constructed wetlands are an established treatment technology for a diverse range of polluted effluents. There is a long history of using wetlands as a unit process in treating acid mine drainage, while recent research has highlighted the potential for wetlands to buffer highly alkaline (pH > 12) drainage. This paper reviews recent evidence on this topic, looking at wetlands treating acidic mine drainage, and highly alkaline leachates associated with drainage from lime-rich industrial by-products or where such residues are used as filter media in constructed wetlands for wastewater treatment. The limiting factors to the success of wetlands treating highly acidic waters are discussed with regard to design practice for the emerging application of wetlands to treat highly alkaline industrial discharges. While empirically derived guidelines (with area-adjusted contaminant removal rates typically quoted at 10 g Fe m²/day for influent waters pH > 5.5; and 3.5-7 g acidity/m²/day for pH > 4 to < 5.5) for informing sizing of mine drainage treatment wetlands have generally been proved robust (probably due to conservatism), such data exhibit large variability within and between sites. Key areas highlighted for future research efforts include: (1) wider collation of mine drainage wetland performance data in regionalised datasets to improve empirically-derived design guidelines and (2) obtaining an improved understanding of nature of the extremophile microbial communities, microbially-mediated pollutant attenuation and rhizospheral processes in wetlands at extremes of pH. An enhanced knowledge of these (through multi-scale laboratory and field studies), will inform engineering design of treatment wetlands and assist in the move from the empirically-derived conservative sizing estimates that currently prevail to process-based optimal design guidance that could reduce costs and enhance the performance and longevity of wetlands for treating acidic and highly alkaline drainage waters.     

Removal of dissolved estrogen in sewage effluents by β-cyclodextrin polymer

Substances with estrogenic activity are found in effluents of municipal sewage plants and dairy farms. These effluents have the potential to induce feminization in male fish. In this study, cyclodextrin polymers (CDPs) that are insoluble in both polar and non-polar solvents were selected for the removal of dissolved estrogens in the effluent of a municipal sewage plant. The removal capacity of CDPs was high in the order of β-CDP ≥ γ-CDP ? α-CDP. The mechanism for adsorption of estrogens to β-CDP was not only due to a host-guest interaction as molecular recognition by β-cyclodextrin (β-CD), but also due to adsorption by the polymer matrix. β-CDP of 0.2% (w/v) removed 17β-estradiol (E2) of about 70% from 10⁻¹¹ mol/L, and more than 90% from ≥ 10⁻¹⁰ mol/L. The removal ratios of E2 in the presence of cholesterols, which are contained at higher concentrations than estrogens in sewage effluents and are adsorptive competitor for β-CDP, were about 85% at a cholesterol/E2 molar ratio of 100 and > 90% at molar ratios of 0.1, 1, and 10. The effluent from a municipal sewage plant had estrogenic activity corresponding to 5.5 × 10⁻¹¹ molE2/L by yeast two-hybrid assay. The estrogens in the effluent were also removed > 90% by the β-CDP treatment. Therefore, β-CDP is able to remove dissolved estrogens over a wide range of concentrations in the presence of various contaminants such as wastewaters.     

Spontaneous electrochemical removal of aqueous sulfide

Most of the existing sulfide removal processes from wastewaters and waste gases require substantial amounts of energy inputs. Here we present an electrochemical method by means of a fuel cell that removes sulfide while producing energy. A lab scale fuel cell was operated at ambient temperature and neutral pH, which was capable of removing aqueous sulfide continuously for 2 months at a rate of 0.62 ± 0.1 kg S m⁻³ d⁻¹ of net anodic compartment (NAC) (0.28 ± 0.05 kg S m⁻³ d⁻¹ of total anodic compartment, TAC). During continuous operation, on average, the power generated was 12 ± 2 W m⁻³ NAC (5 ± 1 W m⁻³ TAC), with a maximum capacity of the cell of 166 W m⁻³ NAC (74 W m⁻³ TAC). Potassium ferricyanide was used as cathodic electron acceptor. Elemental sulfur was identified as the predominant final oxidation product that was deposited on the anode. In this abiotic fuel cell, the sulfide oxidation rate was not diminished by the presence of an organic electron donor (acetate) during batch experiments while the acetate concentration remained unchanged. This is particularly important for selective sulfide removal from wastewater where organics are essential for downstream nutrient removal. Elemental sulfur deposited on the anode appeared to limit the operation of the fuel cell after 3 months of operation, necessitating periodic removal of the accumulated sulfur from the electrode.     

Relative distribution of Pb2+ sorption mechanisms by sludge-derived biochar

Lead sorption capacity and mechanisms by sludge-derived biochar (SDBC) were investigated to determine if treatment of acid mine drainage (AMD) containing metals with SDBC is feasible. It was found that the biochar derived from pyrolysis treatment of sewage sludge could effectively remove Pb²⁺ from acidic solution with the capacities of 16.11, 20.11, 24.80, and 30.88 mg g⁻¹ at initial pH 2, 3, 4 and 5, respectively. Lead sorption processes were pseudo-second order kinetic and faster at a higher pH. Furthermore, the relative contribution of both inorganic mineral composition and organic functional groups of SDBC for Pb²⁺ removal mechanisms, was quantitatively studied at pH 2-5. The results showed that Pb sorption primarily involved the coordination with organic hydroxyl and carboxyl functional groups, which was 38.2-42.3% of the total sorbed Pb varying with pH, as well as the coprecipitation or complex on mineral surfaces, which accounted for 57.7-61.8% and led to a bulk of Ca²⁺ and Mg²⁺ release during sorption process. A new precipitate was solely observed on Pb-loaded SDBC as 5PbO·P₂O₅·SiO₂(lead phosphate silicate) at initial pH 5, confirmed by XRD and SEM-EDX. The coordination of Pb²⁺ with carboxyl and hydroxyl functional groups was demonstrated by FT-IR, and the contribution of free carboxyl was significant, ranging from 26.1% to 35.5%. Results from this study may suggest that the application of SDBC is a feasible strategy for removing metal contaminants from acid solutions.     

Boron-doped diamond anodic treatment of olive mill wastewaters: Statistical analysis, kinetic modeling and biodegradability

The electrochemical treatment of olive mill wastewaters (OMW) over boron-doped diamond (BDD) electrodes was investigated. A factorial design methodology was implemented to evaluate the statistically important operating parameters, amongst initial COD load (1000-5000 mg/L), treatment time (1-4 h), current intensity (10-20 A), initial pH (4-6) and the use of 500 mg/L H₂O₂ as an additional oxidant, on treatment efficiency; the latter was assessed in terms of COD, phenols, aromatics and color removal. Of the five parameters tested, the first two had a considerable effect on COD removal. Hence, analysis was repeated at more intense conditions, i.e. initial COD values up to 10,000 mg/L and reaction times up to 7 h and a simple model was developed and validated to predict COD evolution profiles. The model suggests that the rate of COD degradation is zero order regarding its concentration and agrees well with an electrochemical model for the anodic oxidation of organics over BDD developed elsewhere. The treatability of the undiluted effluent (40,000 mg/L COD) was tested at 20 A for 15 h yielding 19% COD and 36% phenols' removal respectively with a specific energy consumption of 96 kW h/kg COD removed. Aerobic biodegradability and ecotoxicity assays were also performed to assess the respective effects of electrochemical treatment.