Co-treatment Process Research Articles

Relationship between Forage Particle Size and Rate of in vitro Digestion Parameters of Alfalfa-based Lamb in Complete Pelleted Diets

Background: Intensive feeding systems for lamb production are based on high concentrations of feed, depending on the type of forage, which can cause digestive disturbances; however, forage particle length (FPL) and size (FPS) can affect the fermentation process and the productive performance of lambs. Intensive feeding systems for lamb production are based on high concentrations of feed, depending on the type of forage, which can cause digestive disturbances; however, forage particle length (FPL) and size (FPS) can affect the fermentation process and the productive performance of lambs. Understanding how the lambs meet these challenges requires a conceptual integration of forage structure, mechanical particle size of forage and microbial fermentation. This synthesis will hopefully contribute to the development of a biomimetic co-treatment process for translating the unique characteristics of digestion into an effective component of biorefineries for the industrial conversion of cellulosic in forage biomass to useful products. Therefore, this study aimed to evaluate the relationship among FPL, degradability of feed in vitro and digestibility of organic materials. Methods: As a laboratory simulation of rumen functions, four alfalfa FPS lengths were studied within the components of integrated feed pellets 0.1 mm, common in the Saudi animal feed market, 5, 10 and 15 mm using the same feed composition, but with different lengths. Result: Cumulative gas production in PSL8 and PSL12 lambs was higher compared with the other two groups, indicating that lengths greater than 15 mm and less than 5 mm affected gas production rates. The effect of FPL on rumen parameters had no effect on the pH of the rumen fluid. There were no significant differences in all values of the main volatile fatty acids acetate, propionate and butyrate and digestibility increased when the FPL ranged from 5 to 10 mm as in the PSL5 and PSL10 groups. Hydrogen levels were significantly higher in the PSL1 and PSL10 groups than in the PSL5 and PSL15 groups. Based on forage size, groups PSL5 to PSL10 showed the possibility of using this type of feed for growing lambs and small ruminants.

Synergistic cotreatment of cooling tower blowdown and produced waters: Techno-economic, sustainability, and optimization systems analyses

A blowdown and produced water cotreatment train design was preliminarily simulated to explore water-energy nexus synergy. This process model was able to provide results concerning water compositions, chemical demand, and energy intensity. The computational expense associated with this simulation made it intractable to use within optimization algorithms for further informative, comprehensive systems analyses. This work details the efforts of developing a framework suitable for the optimization of computationally demanding wastewater treatment train simulations, specifically demonstrated for the cotreatment train’s process, economic, and sustainability models. The unique challenges of the cotreatment train model motivated a modified surrogate optimization methodology to be developed. Using this framework, worst and best case economic scenarios were optimized to minimize the levelized cost of water (LCOW) employed in a reduced-order model-based simulation. Applying the optimal designs obtained from the surrogate optimization into the original comprehensive simulation resulted in an expected range of LCOW from $2.01 to $4.43m-3. Other established techno-economic and sustainability indicators further inform on process implications. The process was compared to current management practices of blowdown water treatment and produced water injection to discuss the advantages and disadvantages of the proposed cotreatment train designed for water reuse. The cotreatment process was estimated to have lower levelized treatment costs but require more chemicals and energy to manage a higher salinity wastewater than pure blowdown water alone. If sustainable management goals motivate produced water remediation, the cotreatment process can be beneficial for the broader scope of water management.

A low-temperature co-treatment of diethylhexyl phthalate-rich polyvinyl chloride and waste copper catalyst by subcritical water (hydrothermal treatment): Dechlorination, recovery of diethylhexyl phthalate and copper

As one of the most widespread plastics in the world, the recycling of diethylhexyl phthalate-rich polyvinyl chloride (DEHP-rich PVC) faces great challenges because of the high levels of Cl and plasticizers. On the other hand, waste copper catalyst (WCC) discharged from various industrial processes is not effectively recycled. In this study, a significant synergistic effect between the DEHP-rich PVC and WCC was found in a subcritical water (SubCW) medium, and a co-treatment of the DEHP-rich PVC and WCC was developed by the SubCW process. The introduction of WCC significantly improved the dechlorination efficiency of the DEHP-rich PVC to 96.03 % at a low temperature of 250 °C. Under the optimal conditions, the leaching of copper from WCC reached a maximum of 81.08 %. Oil products included DEHP (55.7 %, GC peak area%), 3-methyl-3-heptene (37.3 %, GC peak area%), and 2-ethyl-1-hexanol (7.0 %, GC peak area%). The dechlorination pathways of the DEHP-rich PVC included hydroxyl substitution and direct dechlorination. HCl released from the DEHP-rich PVC led to a decrease in the pH of the system and significant copper leaching from the WCC. DEHP was decomposed by hydrolysis, dehydration, and rearrangement reaction by the SubCW co-treatment process. The enhancement mechanism of the WCC for the dechlorination of the DEHP-rich PVC was based on that the conversion of copper species in the SubCW promoted the formation of hydroxyl radicals and the hydroxyl substitution for chlorine in PVC molecular chain. The proposed SubCW low-temperature co-treatment could be a prospective strategy for the low-energy and synchronous recovery of the two different wastes of the DEHP-rich PVC and WCC.

A novel subcritical water synergistic co-treatment of brominated epoxy resin and copper-based spent catalysts: debromination, phenol production, and copper recovery

In this study, a high-efficiency co-treatment strategy for brominated epoxy resin (BER) and copper-based spent catalyst (CBSC) was developed by using subcritical water (SubCW) process. Multivalent species of copper released from CBSC could accelerate the electron transfer of the SubCW system and efficiently catalyze radical reactions to promote the debromination and decomposition of BER, and had an effect on the capture and binding of bromine species. Meanwhile, the formation of HBr by the BER debromination resulted in a decrease in the system pH and markedly enhanced the leaching/recovery of Cu from CBSC. The optimal conditions of the SubCW co-treatment process were as follows: reaction temperature of 350 °C, solid-to-liquid ratio of 1:30 g/mL, BER-to-CBSC mass ratio of 10:1 g/g, and reaction time of 60 min. Under the optimal conditions, 97.12 % of the Br could be removed from BER by the SubCW co-treatment process and a high-purity phenol (64.09 %) could be obtained in the oil phase product, and 86.44 % of Cu in the CBSC could be leached and recovered. The introduction of CBSC significantly changed the decomposition path of BER. Compared to the SubCW process without CBSC, bromine-free oils products could be obtained by the co-treatment process of BER and CBSC at low-temperature. This study provided a novel understanding of resource conversion mechanism of BER and CBSC in subcritical water medium via the synergistic effect between the two different waste streams to improve treatment efficiency and synchronously recover high-value products.

Coupling pretreatment of ultraviolet/ferrate (UV/Fe(vi)) for improving the ultrafiltration of natural surface water.

Ultrafiltration (UF) is a high-potential technology for purifying natural surface water; however, the problem of membrane fouling has limited its widespread application. Herein, ultraviolet (UV)-activated ferrate (Fe(vi)) was used to purify natural surface water and improve the performance of the UF membrane. The combination of UV and Fe(vi) could generate active species (Fe(v), Fe(iv), ˙OH and O2˙-) to degrade pollutants, while the in situ produced Fe(iii) had the effect of coagulation. With the above action, pollutants were removed, and the pollution load of natural surface water was reduced. After treatment with the UV/Fe(vi) system, dissolved organic carbon was reduced by 49.38%, while UV254 was reduced by 45.00%. The removal rate was further increased to 54.88% and 51.67% after UF treatment. In addition, the fluorescent organics were reduced by 44.22%, and the molecular weight of the organics became smaller. In the stage of UF, the terminal J/J0 was increased from 0.61 to 0.92, and the membrane fouling resistance was decreased by 85.94%. The analysis of the membrane fouling mechanism indicates that the role of cake filtration was weakened among all the mechanisms. Fourier transform infrared spectroscopy showed that less pollutants were accumulated on the membrane surface, and scanning electron microscopy revealed that the membrane pore blockage was relieved. In summary, the UV/Fe(vi) co-treatment process proposed in this study can significantly improve the purification efficiency of the UF systems in natural surface water treatment.

Synergistic cotreatment of cooling tower blowdown and produced waters: Modeling strategies for a comprehensive wastewater treatment simulation

Cooling tower blowdown from thermoelectric power plants and produced water from hydraulic fracturing may soften when mixed due to the complimentary chemistry of the two wastewaters. The potential benefit of low effort softening warrants the investigation of a cotreatment process concerning these industrial wastewaters. The synergy is expected to lessen chemical demand for softening and further enable sustainable practices such as designing for a zero-liquid discharge (ZLD) process. The treatment process may then provide a treated effluent suitable for use as blowdown makeup. In this study, the feasibility and effectiveness of a cotreatment train is explored through simulation of chemical softening, filtration, reverse osmosis (RO), multi-effect distillation (MED), and electrolysis unit operations within a comprehensive process model. Innovative modeling strategies are necessary to result in a meaningful process model when considering the significant complexity of the water chemistry for this treatment train. Through the methodology described in this work, a feasible process design is presented as a base case for treatment of experimentally characterized blowdown and produced water samples obtained in the northern Appalachian region. Thereafter, the base case also establishes a platform for more detailed process analyses of different scenarios in future work. Detailed descriptions of modeling methodologies, process design decisions, and simulation results are provided as a perspective on comprehensive modeling of multi-technology treatment trains for complex feedwaters. With the results of the cotreatment simulation, it is determined that the total water recovery of the process may serve to completely makeup the blowdown rate and partially make up the evaporative losses of a theoretical thermoelectric plant's water demand. This complete recovery is evaluated to require 18,343.531 kW of a chemical energy equivalent, 1184.971 kW of electricity, and 68,126.291MJh−1 of power plant steam to result in 408.532m3h−1 of treated water effluent at a quality of approximately 0.135gL−1 total dissolved solids for the base case design.

Co-treatment of spent automotive catalyst and copper-bearing electroplating sludge to alloy platinum group metals with base metal matrices

Spent automotive catalyst (SAC) is an important secondary metal resource of platinum group metals (PGMs). However, the traditional smelting process for recovering valuable metals from SAC generally has the problems such as high reagents consumption and increased solid waste. Thus, a novel co-treatment process of SAC and copper-bearing electroplating sludge (CBES) was proposed in this study, where CBES was first used as the capture agent and fluxing material in the pyro-capture process of PGMs. The effects of separation behaviors of PGMs and copper under different smelting conditions were studied systematically. The optimum conditions for this process are as follows: m(CBES)/m(SAC) of 2.0, m(SiO2)/m(Al2O3) of 3.00, basicity of 0.80, 5.0 wt% Na2B4O7, oxidative temperature of 1460 ℃, oxidative time of 30 min, NC/Cu of 1.250, reductive temperature of 1300 ℃, and reductive time of 90 min. Under these conditions, the sulfur removal rate exceeds 99% while the recoveries of Pt, Pd, Rh and Cu are 99.26%, 98.53%, 99.96% and 97.60%, respectively. The addition of pure reagents is only about 47% of the total waste mass. Furthermore, the capture process of Cu-Fe alloy for PGMs was discussed, which can consist of three steps: reduction of copper and iron, mutual migration and collision of the reduced metal atoms, and alloying. Finally, the produced slag was synthesized into non-hazardous glass-ceramics material successfully. To sum up, this study achieved the efficient recycling of two hazardous wastes simultaneously.

Mineralization behavior and strengthening technology of high calcium MSWI fly ash in sintering co-treatment process

Co-processing of municipal solid waste incineration fly ash (MSWI-FA) during iron ore sintering is a potentially feasible path for harmless and resourceful utilization. In this paper, the mineralization behavior of high calcium water-washed municipal solid waste incineration fly ash (WM-FA) during iron ore sintering was studied through high temperature in-situ, diffusion couple and sintering experiments, and the corresponding regulation technology was put forward. When adding 1.0 wt.% WM-FA, the tumbler index of sinter was slightly reduced from 69.20% to 68.82%. This index dropped to 62.43% with increasing the proportion of WM-FA to 2.0 wt.%. Potential reason indicated that WM-FA showed higher soft melting temperature than that of sintering mixture, resulted in its insufficient mineralization property. By adding 20 wt.% iron ore into the WM-FA pellets, the mineralization reaction inside and outside WM-FA was significantly improved, and a large amount of CaO·Fe2O3 liquid phase was formed. The tumbler index of sinter increased from 62.43% to 68.35%. Research findings provides a certain theoretical basis for the treatment of municipal solid waste incineration fly ash in the sintering process, and is of great significance to the green and sustainable development of iron and steel industry and cities.

Recovery of platinum and synthesis of glass–ceramic from spent automotive catalyst via co-treatment process with coal fly ash

Recovery of platinum and synthesis of glass–ceramic from spent automotive catalyst via co-treatment process with coal fly ash

Co-treatment of copper smelting slag and gypsum residue for valuable metals and sulfur recovery

Copper smelting slag and gypsum residue are by-products in copper making processes, and both contain valuable elements, such as copper, sulfur, etc. However, there is more than 0.25 wt% Cu in the smelting slag, which cannot be recovered with present technologies. A sulfidation process, which used the gypsum residue as the sulfur resource, was proposed and studied in treating copper smelting slag. Obtained results showed: 1) CaSO4 transformed to CaS under reductive decomposing conditions, and reactions between CaS and slag components occurred spontaneously during the slag cooling process; 2) the Fe/SiO2 mass ratio of the slag, the CaS excess coefficient (α), and the cooling rate (v) had an influence on the terminal phase composition, sulfide particle size, etc.; 3) under optimized conditions (Fe/SiO2=1.0: α=5, v = 1.00°C/min; Fe/SiO2=1.3: α=4, v = 0.25°C/min; Fe/SiO2=1.8: α=5, v = 0.25°C/min), the Cu contents in non-sulfide phases were lower than 0.08 wt%, and the mean particle size of sulfides were 37- 40 μm, which were feasible for flotation recoveries. TCLP (Toxicity Characteristic Leaching Procedure) tests indicated that the co-treatment process improved the stability of these starting materials. Based on samples characterization and thermodynamic analysis, a corresponding reaction mechanism was proposed.

Sulfidogenic fluidized-bed bioreactor kinetics for co-treatment of hospital wastewater and acid mine drainage

A passive co-treatment of acid mine drainage and hospital wastewater previously demonstrated a promising bioremediation viable approach for both toxic streams. The study of inhibition kinetics and microbial communities is essential to understand better the diverse species and the reaction mechanisms within the system. The kinetics and microbiology diversity in the sulfidogenic fluidized-bed reactor (at 30 °C) for co-treatment of hospital wastewater and metal-containing acidic water were examined. The alkalinity from organic oxidation raised the pH of the effluent from 2.3 to 6.1–8.2. Michaelis-Menten modeling yielded (Km =7.3 mg/l, Vmax = 0.12 mg/l min−1) in the batch bioreactor treatment using sulfate-reducing bacteria. For COD oxidation, the dissolved sulfide inhibition constant (Ki) was 3.6 mg/l, and the Ki value for H2S was 9 mg/l. The dominant species in the treatment process belong to the Proteobacteria group (especially Deltaproteobacteria). The ibuprofen and diclofenac compounds achieved the highest removal rates in the bioreactor of 58.6% and 52.3%, respectively; while, ketoprofen and naproxen of 41.9% and 46.6%, respectively. The findings in COD kinetics, sulfate-reducing bacteria abundance, and selected pharmaceutical concentration reduction provide insight into this co-treatment process's capability.

Assessment of mixed matrix membranes (MMMs) incorporated with graphene oxide (GO) for co-treatment of wastewater and landfill leachate (LFL) in a membrane bioreactor (MBR)

Membrane bioreactors show promising features for the co-treatment process of landfill leachate (LFL) and wastewater. However, the high fouling potential of the membranes is still a challenge for treating LFL. A promising approach for membranes fouling mitigation is the incorporation of hydrophilic nanostructures such as graphene oxide (GO) in the structure of polymeric membranes. Nonetheless, long-term tests with GO-incorporated membranes for the treatment of high-strength wastewater under practical conditions are still missing. Thus, in the present study, membranes of polyethersulfone (PES) and PES-GO were synthesized by phase inversion method and successfully implemented in a lab-scale MBR system for LFL and synthetic wastewater co-treatment. Preliminary membrane characterization revealed that the addition of GO resulted in a more restrictive and hydrophilic superficial layer. These properties contributed for PES-GO to obtain high rejection and antifouling properties for humic acid (HA) and bovine serum albumin (BSA) in model solutions. However, no significant differences in the performance of PES-GO and PES membranes for organic removal were observed during the MBR operation. PES-GO exhibited enhanced adsorptive anti-fouling potential which resulted in an increase of the reversible fouling ratio when compared to PES. Though, the incorporation of GO had a low impact on the external anti-fouling potential, which could be resulted from the complex characteristics of LFL. Regarding membranes stability after long exposure to sodium hypochlorite solution, PES-GO exhibited loss of hydrophilicity and presented significant indication of pitting-like damage on the active layer, which could be associated with the GO oxidation by chlorine. Thereby, the findings of this study can be used to develop future strategies involving the use of GO-incorporated membranes in MBRs for the treatment of LFL and complex wastewater.

Co-treatment of electroplating sludge, copper slag, and spent cathode carbon for recovering and solidifying heavy metals

Electroplating sludge, a hazardous solid waste product of the electroplating industry, presents a serious environmental pollution risk. In this study, an environmentally friendly process for solidifying and recovering heavy metals from electroplating sludge using copper slag and spent cathode carbon is proposed. Combining the results of toxicity characteristic leaching procedure tests, thermodynamic analysis, chemical analysis, X-ray diffraction analysis, and electron probe microanalysis, the Cr, Ni, Cu, Fe, and F transformation mechanisms were first probed during vitrification. Under optimal experimental conditions, the Cr, Ni, and Cu recovery ratios reached 75.56 wt%, 98.41 wt%, and 99.25 wt%, and they increased by 40%, 5%, and 5%, respectively compared with the currently utilized technique. Moreover, the toxicity leaching results of the slag indicate that the Cr, F, and Cu are stable, while Ni is easily leached from the (Fe,Ni)(Fe,Cr)2O4 and alloy phases. Under the optimal metal recovery conditions, the leaching concentrations of Cr, Cu, F, and Ni were 0.57 mg/L, 4.45 mg/L, 1.52 mg/L, and 1.85 mg/L, respectively, which can be reused in other materials, minimizing the environmental risk. The electroplating sludge, copper slag, and spent cathode carbon co-treatment process achieves waste disposal with waste and significantly reduces electroplating sludge processing costs.

A potential industrial waste–waste co-treatment process of utilizing waste SO2 gas and residue heat to recover Co, Ni, and Cu from copper smelting slag

A potential industrial waste-waste co-treatment process was proposed and verified for the recovery of the valuable metals Co, Ni, and Cu from copper smelting slag by utilizing high temperature SO2 off-gas. Sulfation roasting followed by water leaching under designed thermodynamic conditions was conducted to facilitate the selective formation of Co, Ni, and Cu sulfates while separating iron as oxide. Several parameters were studied such as roasting temperature, roasting time, the addition of Na2SO4, and leaching agent. Under the optimized sulfation roasting conditions (Gas flow: 500 mL/min, 5% SO2 +20% O2 +75% Ar; Roasting temperature: 650 °C; Roasting time: 4 h; Addition of Na2SO4: 30%) followed by water leaching (Leaching temperature: 80 °C; Leaching time: 5 h; solid to liquid ratio: 0.05 g/mL), the extraction yields of Ni, Co, and Cu were shown to reach 95.8% and 91.8%, 81.6%, respectively. Furthermore, the sulfation roasting – water leaching process was confirmed on lab-scale as a feasible and efficient way to recover valuable metals and the mechanism was determined and verified from the microstructural evolution. Finally, a potential environmentally friendly industrial process in terms of the energy flow and material flow was presented based on preliminary assessments for environmental benefits, economic benefits, and heat recovery.

Economic analysis on sewage sludge drying and its co-combustion in municipal solid waste power plant

Co-treatment in municipal solid waste power plant has been deemed to one of the most suitable ways to handle sewage sludge. Economy of the co-treatment process is very concerned in the waste incineration plant. Thermal calculation of sewage sludge co-combustion was done. Four common sludge drying schemes was compared: flue gas drying, steam drying, electric heating drying in the waste incineration plant and in situ electric heating drying in the sewage treatment plant. Sensitivity analysis was also performed. When the water content was 30–40% and the absolute-dry sludge ratio was 2–3%, the boiler efficiency was reduced by 0.56–1.12% compared with the case without mixing sludge, and the power generation decreased by 0.2568–0.3767 MW in steam drying scheme and by 0.0037–0.0094 MW in other schemes. Net present value (NPV) of flue gas drying was the highest among the four sludge drying schemes, which was more than 20 ¥ million, while the scheme of electric heating drying in the waste incineration plant had the lowest NPV, which can't recoup the initial investment. Sensitivity coefficient of flue gas drying was smallest among different schemes, showing that the risk of this program was the smallest. Absolute-dry sludge ratio and unit subsidy for sludge treatment were sensitive factors for NPV in flue gas scheme, which had a sensitivity coefficient of 1.123–1.171 and 1.232, respectively. Operating parameters optimization of co-combustion of sludge was done and ways to improve economic efficiency was discussed.

Plasma vitrification and heavy metals solidification of MSW and sewage sludge incineration fly ash

Thermal plasma treatment has been considered as one of promising methods for fly ash disposal. In this study, firstly, the characteristics of municipal solid waste incineration (MSWI) fly ash and sewage sludge incineration (SSI) fly ash were analyzed, followed by the raw material formulations of low melting temperature determined by thermodynamic equilibrium calculation. Then verified experiments were carried out by thermal plasma system, focused on the formation condition of vitrified slags with various CaO-SiO2-Al2O3 ratios and the influence factors of heavy metals (Cd, Cr, Ni, Pb, Zn, Cu) transference. According to the results: During the co-treatment process of fly ashes, a lower temperature of vitrified slag formation as low as 1230 ℃ was observed. Vitrification is determined by the molten phase content during melting process, the correlation coefficient between the glass phase content of slag and the molten phase content was 0.81 (P < 0.01). CaO content of raw materials was a major element for the volatilization of Cd and Pb. High Al2O3 content can remain more Cr, Cu and Ni in slags, but it is not conducive to the solidification of Zn. The synthetic toxicity index of heavy metals would greatly reduce from 23153.15 to 663.29–820.63 after thermal plasma treatment.

Combining thermophilic aerobic reactor (TAR) with mesophilic anaerobic digestion (MAD) improves the degradation of pharmaceutical compounds

The removal efficiency of nine pharmaceutical compounds from primary sludge was evaluated in two different operating conditions: (i) in conventional Mesophilic Anaerobic Digestion (MAD) alone and (ii) in a co-treatment process combining Mesophilic Anaerobic Digestion and a Thermophilic Aerobic Reactor (MAD-TAR). The pilot scale reactors were fed with primary sludge obtained after decantation of urban wastewater. Concerning the biodegradation of organic matter, thermophilic aeration increased solubilization and hydrolysis yields of digestion, resulting in a further 26% supplementary removal of chemical oxygen demand (COD) in MAD-TAR process compared to the conventional mesophilic anaerobic digestion. The highest removal rate of target micropollutants were observed for caffeine (CAF) and sulfamethoxazole (SMX) (>89%) with no substantial differences between both processes. Furthermore, MAD-TAR process showed a significant increase of removal efficiency for oxazepam (OXA) (73%), propranolol (PRO) (61%) and ofloxacine (OFL) (41%) and a slight increase for diclofenac (DIC) (4%) and 2 hydroxy-ibuprofen (2OH-IBP) (5%). However, ibuprofen (IBP) and carbamazepine (CBZ) were not degraded during both processes. Anaerobic digestion affected the liquid-solid partition of most target compounds. Sorbed fraction of pharmaceutical compounds on the sludge tend to decrease after digestion, this tendency being more pronounced in the case of the MAD-TAR process due to much lower concentration of solids.

Life Cycle Impact and Benefit Trade-Offs of a Produced Water and Abandoned Mine Drainage Cotreatment Process

A cotreatment process for produced water and abandoned mine drainage (AMD) has been established and demonstrated at the pilot-scale. The present study evaluates the potential of the proposed process to aid in management of two high volume wastewater resources in Pennsylvania. A systems-level approach is established to evaluate the primary trade-offs, including cotreatment process environmental impacts, transportation impacts, and environmental benefits realized from precluding direct AMD release to the environment. Life cycle impact assessment was used to quantify the environmental and human health impacts as well as to identify "hot spots" of the cotreatment process. Electricity use was found to be the dominant contributor to all impact categories. Extending the system boundary to include transportation of the two wastewaters to a to-be-determined cotreatment site revealed the important impact of transportation. An optimization approach was employed (using the region of Southwest Pennsylvania) to evaluate minimization of transportation distance considering the location and number of treatment sites. Finally, a quantitative analysis of environmental benefits realized by precluding direct AMD release to the environment was performed. The results suggest that the magnitude of benefit realized in treating a highly polluted AMD is greater than the magnitude of impacts from the cotreatment process.

Effect of a co-substrate supply in a MBR treating shipboard slop: Analysis of hydrocarbon removal, biomass activity and membrane fouling tendency

The paper reports the main results of an experiment carried out on a membrane bioreactor (MBR) plant designed for the treatment of shipboard slops. With a view of a co-treatment process of the slop with other wastewaters, sodium acetate, as external co-substrate, was supplied (high dosage – Period 1, low dosage – Period 2) to evaluate its effects on hydrocarbons removal. The MBR pilot plant enabled approximately 99% of total petroleum hydrocarbon (TPH) removal during the entire experiment, confirming the robustness of the MBR technology for the treatment of slops. The chromatography/mass spectrometry analysis showed that the removal efficiency for each alkane was close to the value observed for total mixture removal (>99%) and the hydrocarbons removal was mostly due to the microorganism-mediated biodegradation. The biological contribution to TPH removal increased from approximately 85% to 98% when the co-substrate was decreased. Biomass kinetics revealed that a lower co-substrate dosage enhanced the growth of bacterial groups able to use hydrocarbons as primary substrate. A clear predominance of Microthrix Parvicella under low co-substrate dosage was observed. However, the lower co-substrate addition caused a significant worsening in the physical properties of the activated sludge, which resulted enriched in soluble exopolymers (>70%), more hydrophobic (>90%) and with small and dispersed flocs (<30 μm). Consequently, the membrane permeability reduced because of the irreversible fouling increase.

Free sulfurous acid (FSA) inhibition of biological thiosulfate reduction (BTR) in the sulfur cycle-driven wastewater treatment process

A sulfur cycle-based bioprocess for co-treatment of wet flue gas desulfurization (WFGD) wastes with freshwater sewage has been developed. In this process the removal of organic carbon is mainly associated with biological sulfate or sulfite reduction. Thiosulfate is a major intermediate during biological sulfate/sulfite reduction, and its reduction to sulfide is the rate-limiting step. In this study, the impacts of saline sulfite (the ionized form: HSO3− + SO32−) and free sulfurous acid (FSA, the unionized form: H2SO3) sourced from WGFD wastes on the biological thiosulfate reduction (BTR) activities were thoroughly investigated. The BTR activity and sulfate/sulfite-reducing bacteria (SRB) populations in the thiosulfate-reducing up-flow anaerobic sludge bed (UASB) reactor decreased when the FSA was added to the UASB influent. Batch experiment results confirmed that FSA, instead of saline sulfite, was the true inhibitor of BTR. And BTR activities dropped by 50% as the FSA concentrations were increased from 8.0 × 10−8 to 2.0 × 10−4 mg H2SO3-S/L. From an engineering perspective, the findings of this study provide some hints on how to ensure effective thiosulfate accumulation in biological sulfate/sulfite reduction for the subsequent denitrification/denitritation. Such manipulation would result in higher nitrogen removal rates in this co-treatment process of WFGD wastes with municipal sewage.