Synthetic Sewage Research Articles

Oxygen mass transfer and post-denitrification in a modified rotating drum biological contactor

A lab-scale rotating drum biological contactor (RDBC) was implemented and accessed concerning abiotic oxygen transfer rate and treatment capacity for domestic sewage. The dissolved oxygen (DO) transfer test showed that the rotational speed and the submergence level of drum greatly affected the DO in bulk liquid with the volumetric oxygen transfer coefficient KLa of 2.3-25.9 h−1, effectively achieving anaerobic/anoxic/aerobic conditions in the reactor. The post-denitrification process was proposed using the RDBC to degrade the synthetic nitrogen-containing sewage wastewater. When the hydraulic retention time was 16 h, the flow distribution ratio was 3:1 and the anoxic rotational speed was 6 rpm, the effluent NH4+-N and TN were 2.3 mg L−1 and 7.3 mg L−1 with the NH4+-N and TN removal efficiency of 94.1% and 80.9%, respectively. The Nitrosomonas europaea and Candidatus Kuenenia dominated in the anoxic carried-biofilm, indicating that the coexisting of aerobic and anaerobic ammonium oxidation bacteria enhanced the TN loss in the post-anoxic tank. This study provides an innovative non-aeration technology for biological wastewater treatment and has implications to simplify operation and save energy.

Reusable magnetic Ag/Fe, N-TiO2/Fe3O4@SiO2 composite for simultaneous photocatalytic disinfection of E. coli and degradation of bisphenol A in sewage under visible light

A visible-light-driven and magnetic photocatalyst Ag/Fe,N-TiO2/Fe3O4@SiO2 (AgFeNTFS) was synthesized through a multi-step method. AgFeNTFS was tested for the photocatalytic disinfection of Escherichia coli (E. coli) and degradation of bisphenol A (BPA) under visible light irradiation, separately and simultaneously. The results showed that a 6.3-log reduction in cell density of E. coli was achieved and BPA (2 mg/L) was completely removed by AgFeNTFS in the separated photocatalytic processes within 120 min. In the simultaneous process, the photocatalytic disinfection of E. coli was not influenced in the presence of BPA, but the efficiency of BPA degradation was dropped by 10%. This was likely due to the competition for the same dominant reactive species of O2− and H2O2 between E. coli and BPA in the simultaneous process, as evidenced by the scavenger study and the interactions between the pollutants and AgFeNTFS. Moreover, the simultaneous photocatalytic activity of E. coli disinfection and BPA degradation by AgFeNTFS was investigated in the sewage obtained from a local wastewater treatment plant. The photocatalysis treated sewage could meet with the local disinfection discharge standard with a 3-log reduction of E. coli after 90 min, and a complete removal of BPA was achieved simultaneously after 360 min. Moreover, AgFeNTFS showed high magnetic separation efficiency and had a good reusability over three cycles for the simultaneous photocatalytic disinfection and degradation of BPA in both synthetic water and sewage. This study provides insights on the application of a reusable magnetic photocatalyst for simultaneous disinfection and degradation of BPA in sewage.

Fast adsorption of chromium (VI) ions from synthetic sewage using bentonite and bentonite/bio-coal composite: a comparative study

Bentonite is a traditional low-cost efficient adsorbent, which has high potential for heavy metal removal from wastewaters due to its abundance, chemical and mechanical stability, high exchange capacity, and unique structural properties. In the present work, bentonite and bentonite/bio-coal composite were synthesized and utilized as a natural, low-cost, and eco-friendly adsorbents for adsorption of chromium (VI) ions from aqueous solutions. Bentonite (Bent) and apricot leaves were used to produce bentonite/bio-coal (Bent/BC) composite. FT-IR, XRD, SEM/EDX map, XRF, TGA and SMB (special surface) analysis were carried out to study the characteristics of these materials. The results showed that Bent and Bent/BC have an appropriate surface and characteristics for adsorption process. The isotherm behavior of adsorption process was investigated using Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherm models. Regarding the correlation coefficient (R2) obtained from isotherm models, it was concluded that the equilibrium behavior of the process is more describable with Langmuir isotherm model than other ones. The maximum adsorption capacity (qe, mg/g) determined by Langmuir isotherm model for Bent and Bent/BC was 59.523 and 64.102 mg g−1 respectively. Based on regression coefficient values, the pseudo-second order was found suitable than first-order kinetic model. Also it has regular behavior of qe.exp with qe.cal. The amount of enthalpy (ΔH°) for the chromium(VI) ions adsorption process using Bent and Bent/BC was determined to be −23.916 and −28.273 kJ mol−1 respectively, which indicates that the adsorption process is exothermic. According to the parameters ΔH°, RL, n and E, it was determined that the chromium (VI) adsorption process using Bent and Bent/BC adsorbents is physical and desirable.

Activation of persulfate by a novel Fe(II)-immobilized chitosan/alginate composite for bisphenol A degradation

In this study, a novel Fe(II) immobilized chitosan/alginate composite (Fe-Chitoal) was prepared via a simple crosslinking reaction to activate persulfate (PS) to degrade bisphenol A (BPA). The newly synthesized Fe-Chitoal was characterized by scanning electron microscopy, energy dispersive spectroscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy, which indicated that Fe was successfully imprinted into the composite. The PS/Fe-Chitoal system demonstrated a much higher removal efficiency of BPA (99.5%) than the conventional PS/Fe(II) system (69.2%) with a negligible amount of Fe ions released into the solution. The effects of different experimental conditions, including the concentration of PS, concentration of Fe-Chitoal, and pH, on the removal of BPA were also investigated. The removal rate increased with increasing amounts of PS and Fe-Chitoal, and a high removal efficiency was maintained at a pH of 2–10. The PS/Fe-Chitoal system was rarely affected by high concentrations of anions (Cl−, SO42−, NO3−, and HCO3−), and the composite catalyst could be reused in a synthetic sewage solution. To simply separate the material, a Fe-Chitoal mesh bag was fabricated, which showed a consistent catalytic reactivity toward PS and BPA removal suggesting practical field applications.

Characterization and Dynamic Shift of Microbial Communities during Start-Up, Overloading and Steady-State in an Anaerobic Membrane Bioreactor.

A lab-scale anaerobic membrane bioreactor (AnMBR) with a side stream tubular membrane was developed to treat synthetic domestic sewage to evaluate its performance and the dynamic shift of bacterial and archaeal communities during the start-up, steady-state, overloading and recovery periods of operation at mesophilic temperatures. During the start-up period, the bacterial and archaeal communities changed drastically, and Proteobacteria and Bacteroidetes predominated. During the steady-state period, the AnMBR exhibited excellent COD removal above 91%, and COD of the effluent was below 50 mg/L. High-throughput sequencing analysis results revealed that bacterial and archaeal communities shifted significantly from the start-up to the steady-state period, and that the Proteobacteria phylum predominated on days 140, 162 and 190, and the archaea community hydrogenotrophic methanogen genus Methanolinea (1.5–6.64%) predominated over the aceticlastic methanogen genus Methanothrix (1.35–3.07%). During the overloading period, significant changes occurred in microbial community on day 210, e.g., the phyla Bacteroidetes (30%), Proteobacteria (23%) and Firmicutes (18%) predominated and the archaeal community was completely suppressed, and Methanobrevibacter (0.7%) was the only methanogen genus that emerged in the overloading period. After a shock loading period, the microbial communities exhibited significant changes within the ranks of methanogens and shifted to dominance of the aceticlastic methanogen pathway. In addition, the TVFAs to alkalinity ratio in this study was suitable as an indicator of monitoring performance in the AnMBR operation.

Biomass pyrolysis: past, present, and future

Biomass pyrolysis is a promising renewable sustainable source of fuels and petrochemical substitutes. It may help in compensating the progressive consumption of fossil-fuel reserves. The present article outlines biomass pyrolysis. Various types of biomass used for pyrolysis are encompassed, e.g., wood, agricultural residues, sewage. Categories of pyrolysis are outlined, e.g., flash, fast, and slow. Emphasis is laid on current and future trends in biomass pyrolysis, e.g., microwave pyrolysis, solar pyrolysis, plasma pyrolysis, hydrogen production via biomass pyrolysis, co-pyrolysis of biomass with synthetic polymers and sewage, selective preparation of high-valued chemicals, pyrolysis of exotic biomass (coffee grounds and cotton shells), comparison between algal and terrestrial biomass pyrolysis. Specific future prospects are investigated, e.g., preparation of supercapacitor biochar materials by one-pot one-step pyrolysis of biomass with other ingredients, and fabricating metallic catalysts embedded on biochar for removal of environmental contaminants. The authors predict that combining solar pyrolysis with hydrogen production would be the eco-friendliest and most energetically feasible process in the future. Since hydrogen is an ideal clean fuel, this process may share in limiting climate changes due to CO2 emissions.

Matrix Effect Assessment of an Ion Chromatographic Method to Determine Inorganic Anions in Wastewater

Inorganic anion monitoring is essential for bioreactor operation and is related for pollution control or energy and products recovery. However, there is a lack of studies validating methods for inorganic anions analyses in conditions compatible to those in bioreactor operations treating different types of wastewater. This paper provides a systematic statistical study and matrix-effect assessment for sugarcane vinasse, leachate, sewage and synthetic sewage. Sample preparation consisted of only a filtration and sample dilution. Cl−, NO2−, NO3−, PO43− and SO42− were determined in a Dionex ICS 5000® equipped with a chemical conductivity suppressor. Calibration curves were linear and well-adjusted between 2.5 and 50 mg L−1 for all the anions in all the tested matrices, except PO43− and SO42− in vinasse. A calibration range for PO43− in all tested matrices was 5.0 to 100 mg L−1, whereas a range from 5.0 mg L−1 to 50 mg L−1 was obtained for SO42− in vinasse. All the anions yielded recoveries in the range of 85–115% for all the tested matrices. Relative standard deviations lower than 10 and 2% were achieved for peak areas and retention times, respectively. A signal enhancement was observed for all the tested matrices and all the anions. The matrix effect level varied from −1.7 (NO2− in vinasse) to −33.9% (Cl− in leachate). Sewage was the less affected matrix, while leachate gave higher matrix effects. Validation results and the matrix effect assessment showed that a simple sample preparation is suitable for multi-elemental analyses of inorganic anions for complex environmental samples.

Cold adaptation and replicable microbial community development during long-term low-temperature anaerobic digestion treatment of synthetic sewage.

ABSTRACTThe development and activity of a cold-adapting microbial community was monitored during low-temperature anaerobic digestion (LtAD) treatment of wastewater. Two replicate hybrid anaerobic sludge bed-fixed-film reactors treated a synthetic sewage wastewater at 12°C, at organic loading rates of 0.25–1.0 kg chemical oxygen demand (COD) m−3 d−1, over 889 days. The inoculum was obtained from a full-scale anaerobic digestion reactor, which was operated at 37°C. Both LtAD reactors readily degraded the influent with COD removal efficiencies regularly exceeding 78% for both the total and soluble COD fractions. The biomass from both reactors was sampled temporally and tested for activity against hydrolytic and methanogenic substrates at 12°C and 37°C. Data indicated that significantly enhanced low-temperature hydrolytic and methanogenic activity developed in both systems. For example, the hydrolysis rate constant (k) at 12°C had increased 20–30-fold by comparison to the inoculum by day 500. Substrate affinity also increased for hydrolytic substrates at low temperature. Next generation sequencing demonstrated that a shift in a community structure occurred over the trial, involving a 1-log-fold change in 25 SEQS (OTU-free approach) from the inoculum. Microbial community structure changes and process performance were replicable in the LtAD reactors.

The mechanism of enhanced wastewater nitrogen removal by photo-sequencing batch reactors based on comprehensive analysis of system dynamics within a cycle

To understand the mechanism of enhanced nitrogen removal by photo-sequencing batch reactors (photo-SBRs), which incorporated microalgal photosynthetic oxygenation into the aerobic phases of a conventional cycle, this study performed comprehensive analysis of one-cycle dynamics. Under a low aeration intensity (about 0.02 vvm), a photo-SBR, illuminated with light at 92.27 μ·mol·m−2·s−1, could remove 99.45% COD, 99.93% NH4+-N, 90.39% TN, and 95.17% TP, while the control SBR could only remove 98.36% COD, 83.51% NH4+-N, 78.96% TN, and 97.75% TP, for a synthetic domestic sewage. The specific oxygen production rate (SOPR) of microalgae in the photo-SBR could reach 6.63 fmol O2·cell−1·h−1. One-cycle dynamics shows that the enhanced nitrogen removal by photo-SBRs is related to photosynthetic oxygenation, resulting in strengthened nitrification, instead of direct nutrient uptake by microalgae. A too high light or aeration intensity could deteriorate anoxic conditions and thus adversely affect the removal of TN and TP in photo-SBRs.

Identification of Nitrate Sources and the Fate of Nitrate in Downstream Areas: A Case Study in the Taizi River Basin

A total of 14 samples were collected in May 2016(dry season)and August 2016 (wet season) in the downstream area of the Taizi River. △15 N-NO3- and △18 O-NO3- were determined using the azide method, and △18 O-H2O was determined using a CO2-H2O equilibration technique. To identify NO3- sources and transformations in the downstream area of Taizi River Basin, ion chromatography, Nessler's reagent spectrophotometry, the azide method, and CO2-H2O equilibration methods were utilized to determine the concentrations of NO3-, Cl-, NH4+-N, and isotopic compositions (△15 N and △18 O) of NO3- and the △18 O-H2O in surface water. The results showed that the NO3- was mainly derived from mixed sources. During the dry season, the nitrate in the surface water was derived from soil nitrogen, manure, and sewage in the upper reaches, and mainly derived from synthetic fertilizer, manure, and sewage in the middle and lower reaches of the Beisha River. The nitrate was mainly derived from manure and sewage in the Nansha River. The nitrate was mainly derived from soil nitrogen in the upper reaches, mainly derived from synthetic fertilizer, manure, and sewage in the middle reaches, and mainly derived from manure and sewage in the lower reaches of the Haicheng River. During the wet season, the nitrate sources in surface water were soil nitrogen, synthetic fertilizer, manure, and sewage in the Beisha River; synthetic fertilizer, manure, and sewage in the middle and lower reaches of the Haicheng River and the Nansha River; and soil nitrogen and synthetic fertilizer in the upper reaches of the Haicheng River. NO3- and NH4+-N concentrations decreased with increasing △15 N-NO3- from the dry season to the wet season, indicating that volatilization of NH4+-N and denitrification of NO3- might occur during the wet season. There is a slightly positive relationship between the reciprocal of the concentration of 1/ρ(NO3-) and △15 N-NO3- during the wet season, indicating that mixing processes occurred in surface water. The results will provide information on nitrate sources during seasonal variations in the plain areas.

Assessing potential impacts of phosphate precipitation on nitrous oxide emissions and the carbon footprint of wastewater treatment plants

ABSTRACTMetal salts are widely used for the precipitation of phosphorus during wastewater treatment transforming soluble orthophosphate to an insoluble salt. In practice, more complex reactions are taking place including a reduction of the chemical solubility of dissolved greenhouse gases, such as nitrous oxide, present in the wastewater stream. In this respect, it was postulated that phosphorous precipitation will lead to artificial N2O stripping and hence to an increased carbon footprint of wastewater treatment plants. From lab-scale experiments utilizing N2O-saturated synthetic sewage solutions, it was evidenced that metal salt addition leads to N2O stripping with 20.8 g N2O per liter for a FeCl2-based precipitant to 26.4 g N2O per liter for a Aln(OH)mCl3n-m-based precipitant. Taking this maximum potential stripping effect into account for a carbon footprint analysis, a potential contribution of 16.11 kg CO2,eq·PE−1·a−1 was calculated in a case study, where FeCl3 was considered. With respect to the defined system boundary conditions, the overall on-site and off-site CO2 emissions were raised by 34% from 46.87 kg CO2,eq·PE−1·a−1 to 62.97 kg CO2,eq·PE−1·a−1 through CO2,eq coming from phosphorous precipitation.

Performances and microbial characteristics of granular sludge for autotrophic nitrogen removal from synthetic and mainstream domestic sewage

The completely autotrophic nitrogen removal over nitrite (CANON) process is an important component of energy self-sufficient sewage treatment plants, and the use of aerobic granular sludge is a profitable choice for the CANON process. In this study, the performance and microbial characteristics of CANON granular sludge were investigated for treating synthetic and mainstream domestic sewage. The average nitrogen removal rate (NRR) was 3.22 kg N m−3 d−1 during the high-rate operating period with high MLSS (4.09 g L−1) and DO (∼1.0 mg L−1) for treating synthetic sewage. When the influent was mainstream sewage, the average NRR was 1.11 kg N m−3 d−1. The effluent nitrate concentration was very low, and nitrate build-up was not found. High-throughput pyrosequencing results indicated that, Nitrosomonas and Candidatus Brocadia were the dominant genus in ammonia oxidizing bacteria (AOB) and anaerobic AOB (AAOB), respectively. The proportions of AOB and AAOB decreased during mainstream sewage treatment, but the reactor maintained good performance. The results confirmed the feasibility of using CANON granular sludge for treating mainstream sewage.

Identification of Nitrate Sources and Transformation Processes in Midstream Areas:A Case in the Taizi River Basin

This study analyzed the nitrate (NO3-), ammonia nitrogen (NH4+-N), chloride (Cl-), δ15 N-NO3-, δ18O-NO3-, and δ18O-H2O in the surface water to identify the nitrate sources and transformation processes in midstream areas of the Taizi River basin in May and August 2016, corresponding to the dry season and wet season, respectively. The results indicated that the NO3-, Cl-, and NH4+-N concentrations and the δ18O-NO3- in the dry season were greater than those in the wet season, and the δ15 N-NO3- did not show significant seasonal variations based on the Man-Whitney U test. The NO3- was derived mainly from the mixed sources according to the ranges of NO3-/Cl-, δ15 N-NO3-, and δ18O-NO3-. The nitrate sources in the surface water were synthetic fertilizer, soil nitrogen, manure, and sewage in the Xihe River (XR), Lanhe River (LR), and Xiada River (XDR) and soil nitrogen and synthetic fertilizer in the Er dao River (EDR) during the wet season. The sources were synthetic fertilizer and soil nitrogen in the XDR and soil nitrogen, manure, and sewage in the XR, LR, and EDR during the dry season. The significant negative relationship between NO3- and NH4+ and the significant positive relationship between NO3- and δ15 N-NO3- in the wet season indicated that the volatilization and nitrification of soil N might be related to NO3- sources in the wet season. NH4+-N and δ15 N-NO3- increased with decreasing NO3- and Cl- in EDR and LR during the wet season, which indicated denitrification processes occurred. There was a significant relationship between NO3- and Cl-, indicating that mixing processes occurred in the surface water during the two sampling periods. This study will provide a better understanding for nitrate sources related to seasonal variations and transformation processes in hilly areas.

Improving energy efficiency and fouling mitigation for membrane bioreactor in Al-Rustamiyah sewage treatment plant based on hydrodynamics

In Al-Rustamiyah sewage treatment plant in the east of Baghdad city, capital of Iraq, the membrane bioreactor suffering from a severe biofouling problem. The main reason for this problem is inefficient and inadequate aeration process. The objective of this work is to control fouling and to improve the energy efficiency of the submerged membrane bioreactor. Fouling control is achieved by optimizing the two-phase hydrodynamic parameters (air bubble diameter and shear stress), while energy efficiency improved through analysis of flow field. An experimental rig similar to real plant was built, and several operating and design parameters were experimentally tested. The parameters were air flow rate (1–9 L/min), membrane sheets spacing (3, 5, and 7 mm), and air diffuser design (pipe diffuser and disk diffuser). The bubble sizes were measured experimentally using high-speed camera. It was found that larger bubbles were produced at narrow channels between the membrane sheets. Optimization using computational fluid dynamic with ANSYS FLUENT was employed; the results showed that a bubble diameter of 2.5 mm had a slug flow pattern, resulting in better energy saving for a 3 mm space between membrane sheets with a 5 L/min air flow, while maximum shear stress obtained was (4 Pa). Nutrients removal results from synthetic sewage were 97.32, 79.68, and 13% for COD, NH3–N, and PO 4 −3 , respectively, at 6 days retention time. The results obtained are quite significant in practice because it contributes to improve the efficiency of membrane bioreactor in Al-Rustamiyah sewage treatment plant.

In situ coagulation versus pre-coagulation for gravity-driven membrane bioreactor during decentralized sewage treatment: Permeability stabilization, fouling layer formation and biological activity

Gravity-driven membrane filtration systems are promising for decentralized sewage treatment due to their low energy consumption and low maintenance. However, the low stable permeability/flux is currently limiting their wider application. With the ultimate goal of increasing permeability, the aim of this study was to evaluate the effect of coagulation (in situ coagulation and pre-coagulation) on the performance of a gravity-driven membrane bioreactor (GDMBR) during treatment of synthetic sewage. Results show that in situ coagulation significantly increased permeability (more than two-fold); however, no stabilization of permeability occurred over the whole operation, when non-coagulated and pre-coagulated reactors were compared. The high permeability observed was attributed to the accumulated aluminium floc in the reactor, which prevented formation of fluorescent microbial metabolites (aromatic and tryptophan proteins, as well as fulvic acids), and further avoided membrane pore blocking. In addition, the surface porosity of the fouling layer was improved (from 11.2% to 32.4% for non-coagulated and in situ coagulated reactors). The unstable permeability was possibly associated with lower biological processes within the fouling layer. These might include lower adenosine triphosphate (ATP) content and lower fluorescent metabolites from the extracellular polymeric substances (EPS) caused by the accumulated Al (compared with the control). On the other hand, pre-coagulation improved the level of stable permeability compared with the control (80 versus 40 L/m2 h bar), mainly because pre-coagulation decreased the EPS content and also maintained high ATP content of the fouling layer. In addition, both coagulation processes reduced the total filtration resistance, mainly the hydraulically reversible resistance and cake layer resistance, which could lower the cleaning frequency. Overall, coagulation could greatly increase the removal efficiency and improve the GDMBR permeability, which would make the process suitable for decentralized wastewater treatment.

Effects of influent C/N ratios and treatment technologies on integral biogas upgrading and pollutants removal from synthetic domestic sewage

Three different treatment technologies, namely mono-algae culture, algal-bacterial culture, and algal-fungal culture, were applied to remove pollutants form synthetic domestic sewage and to remove CO2 from biogas in a photobioreactor. The effects of different initial influent C/N ratios on microalgal growth rates and pollutants removal efficiencies by the three microalgal cultures were investigated. The best biogas upgrading and synthetic domestic sewage pollutants removal effect was achieved in the algal-fungal system at the influent C/N ratio of 5:1. At the influent C/N ratio of 5:1, the algal-fungal system achieved the highest mean chemical oxygen demand (COD) removal efficiency of 81.92% and total phosphorus (TP) removal efficiency of 81.52%, respectively, while the algal-bacterial system demonstrated the highest mean total nitrogen (TN) removal efficiency of 82.28%. The average CH4 concentration in upgraded biogas and the removal efficiencies of COD, TN, and TP were 93.25 ± 3.84% (v/v), 80.23 ± 3.92%, 75.85 ± 6.61%, and 78.41 ± 3.98%, respectively. These results will provide a reference for wastewater purification ad biogas upgrading with microalgae based technology.

MICROCOSM EXPERIMENTS ON A COCONUT-FIBRE BIOFILM TREATMENT SYSTEM TO EVALUATE WASTE WATER TREATMENT EFFICIENCIES

Interest in utilization of locally available biomasses as biofilm support media for wastewatertreatment in developing countries is increasing. In this study, microcosm experiments on a coconut-fibrebiofilm treatment system were carried out to evaluate wastewater treatment efficiencies in the laboratory usingtwo wastewaters, synthetic sewage and leachate, with different pollutant loads. Three coconut-fibre conditionswere set as a single bundle (low fibre density: LFD), two bundles (high fibre density: HFD), and no coconutfibre (blank). The wastewater was first circulated in the system for six weeks (circulation stage) and thendischarged from the treatment tank for 7–24 weeks (treatment stage). Water quality parameters of effluents,pH, DO, EC, BOD, COD, TC, and TN, were measured at one-week intervals, and the sedimented sludge ineach treatment tank was collected to determine C, N, and P contents. Results showed effective reductions inBOD and COD in the LFD and HFD conditions for the synthetic leachate, indicating that the coconut fibrecontributed to the treatment of wastewater. On the other hand, the fibre density had less or no effect on thereduction of water quality parameters in the synthetic sewage. For both synthetic sewage and leachate, the Cand N consumptions generally increased in the order of blank, LFD, and HFD. In particular, sludgesedimentation contributed to C consumption under the HFD condition.

Removal of selected pharmaceuticals in an anaerobic membrane bioreactor (AnMBR) with/without powdered activated carbon (PAC)

The removal of five selected pharmaceutical compounds was investigated in a lab-scale anaerobic membrane bioreactor (AnMBR) treating synthetic sewage. Trimethoprim (Tmp) and sulfamethoxazole (Smx) were consistently removed at efficiencies of 94.2±5.5%, and 67.8±13.9%, respectively, while in contrast, only marginal removals of carbamazepine (Cbz) (0.3±19.0%) and diclofenac (Dcf) (15.0±7.2%) were achieved. Finally, three distinct stages of triclosan (Tcs) removal were observed: 82.3±15.0% within the first 10days; 54.4±10.4% in the following 30days; and 31.4±12.6% in the last 30days. Adsorption to the sludge was the major contributing factor for its initial high removal. When powdered activated carbon (PAC) was added to the AnMBR, the removal of all five pharmaceuticals improved, especially for Smx and Tcs, which showed removal efficiencies of 95.5±4.6% and 93.2±6.6%, respectively. Higher removals of Cbz (92.4±5.3%) and Dcf (82.6±11.1%) were also observed, but only within the initial 5days of PAC addition, and enhancement in their biotransformation by PAC adsorption was determined to be the major contributing factor for these improved removals.

Seawater-based wastewater accelerates development of aerobic granular sludge: A laboratory proof-of-concept

This study aimed to develop an aerobic granular sludge process for the efficient treatment of highly saline wastewater and understand the granulation process in a seawater-based multi-ion matrix. Five identical sequencing batch airlift reactors (SBARs) are used to treat synthetic saline sewage with different proportions of real seawater (0%–100%). The results confirm that aerobic granular sludge can be successfully developed with various proportions of seawater up to 100% and show that seawater not only significantly accelerates granulation but also generates stronger granular structures than does freshwater. The increased presence of gel-forming alginate-like exopolysaccharides in the granules explains why a greater proportion of seawater leads to higher density and improves the cohesive strength of the granules. SEM-EDX analysis further revealed substantial presence of both Ca2+ and Mg2+ phosphate in the granule core as well as in the outer layers providing extra bridging forces in addition to alginate-like exopolysaccharides for accelerating the granule formation and maintaining the structure. It is hoped that this work could explore another approach for saline sewage treatment and bring some clues for the mystery of granulation mechanism.

Tackling the salinity-pollution nexus in coastal aquifers from arid regions using nitrate and boron isotopes.

Salinization and nitrate pollution are generally ascertained as the main issues affecting coastal aquifers worldwide. In arid zones, where agricultural activities also result in soil salinization, both phenomena tend to co-exist and synergically contribute to alter groundwater quality, with severe negative impacts on human populations and natural ecosystems' wellbeing. It becomes therefore necessary to understand if and to what extent integrated hydrogeochemical tools can help in distinguishing among possible different salinization and nitrate contamination origins, in order to provide adequate science-based support to local development and environmental protection. The alluvial plain of Bou-Areg (North Morocco) extends over about 190km2 and is separated from the Mediterranean Sea by the coastal Lagoon of Nador. Its surface is covered for more than 60% by agricultural activities, although the region has been recently concerned by urban population increase and tourism expansion. All these activities mainly rely on groundwater exploitation and at the same time are the main causes of both aquifer and lagoon water quality degradation. For this reason, it was chosen as a case study representative of the typical situation of coastal aquifers in arid zones worldwide, where a clear identification of salinization and pollution sources is fundamental for the implementation of locally oriented remedies and long-term management strategies. Results of a hydrogeochemical investigation performed between 2009 and 2011 show that the Bou-Areg aquifer presents high salinity (often exceeding 100mg/L in TDS) due to both natural and anthropogenic processes. The area is also impacted by nitrate contamination, with concentrations generally exceeding the WHO statutory limits for drinking water (50mg/L) and reaching up to about 300mg/L, in both the rural and urban/peri-urban areas. The isotopic composition of dissolved nitrates (δ15NNO3 and δ18ONO) was used to constrain pollution drivers. The results indicate two main origins for human-induced pollution: (i) manure and septic effluents, especially in urban areas, and (ii) synthetic fertilizers in agricultural areas. In the latter, δ15N-enriched values highlight a mixture of those sources, possibly related to unbalanced fertilization and agricultural return flow. Boron isotopes (δ11B) were hence studied to further distinguish the nitrate origin in the presence of multiple sources and mixing processes. The results indicate that in the study area, the high geochemical background for B and Cl, associated to the complex water-rock interaction processes, limit the application of the coupled δ11B and δ15N isotopic systematics to the detection of sources of groundwater pollution. In fact, despite the exceedingly high nitrate contents, the depleted δ11B values that characterize synthetic fertilizers and sewage leakages could not be detected. Therefore, even if in saline groundwater the anthropogenic contribution has a negligible effect in terms of salinity input, with both sewage and irrigation water not very charged, the associated nitrate content fuels up water-rock interaction processes, eventually leading to a mineralization increase.