Excess Sludge Research Articles

An enhanced rural anoxic/oxic biological contact oxidation process with air-lift reflux technique to strengthen total nitrogen removal and reduce sludge generation

Biological contact oxidation process is attractive and widely used in rural sewage treatment, due to its simplicity and relatively superior pollutants elimination efficiency. However, the effluent total nitrogen (TN) and excess sludge yield during the biological contact oxidation process still need to be intensified to stably satisfy the discharge standard. In the current study, an enhanced rural anoxic/oxic (A/O) biological contact oxidation process with air-lift reflux technique was properly established, which achieved better pollutant removal efficiency and lower excess sludge yield. Under the pathway of air-lift reflux technique, the TN and ammonia nitrogen (AN) removal capacity of A/O biological contact oxidation process were obviously increased from 66.5% and 73.8% to 95.3% and 80.6%, respectively, which should be attributed to the increasement of nitrifying bacteria (Nitrospira and Nitrosomonas) and denitrifying bacteria (Denitratisoma, Thauera, and Dechloromonas). The excess sludge yield was also decreased from 0.19 kg MLSS/kg COD (no reflux model) to 0.11 kg MLSS/kg COD (air-lift reflux model) since the degradation of returned oxic sludge in the anoxic tank, which was verified by stable isotope tracer analysis. The rural A/O biological contact oxidation process with air-lift reflux technique had great potential to strengthen TN removal and reduce sludge generation, which could provide a useful and easy-implement technology for rural sewage treatment.

Controlling factors and involved mechanisms on forming alginate like extracellular polymers in flocculent sludge

Alginate like extracellular polymers (ALE) recovered from excess sludge have been evaluated as an eco-friendly, cost effective and sustainable alternative to highly valued materials. However, the ALE extraction from flocculent sludge ranges normally from 90 to 190 mg/g VSS, which is only equivalent to the lowest edge of the ALE production from aerobic granular sludge (AGS). But flocculent sludge is much higher in production than AGS and thus a further investigation was expected on key factors and associated mechanisms controlling ALE formation of flocculent sludge. The investigation was conducted by lab-scale sequencing batch bioreactors. The experiments revealed that flocculent sludge with starch used as an influent substrate contained the highest ALE production (220.3 ± 8.0 mg/g VSS). Low temperature was favorable to enriching ALE, up to 303.3 ± 21.5 mg/g VSS at 12 °C. Moreover, ALE reached up to 137.8 ± 13.2 mg/g VSS at C:N = 5:1 and slightly declined with increased or decreased the C/N ratio. The specific ALE yield was 63.7 mg ALE/(g BOD5) at a low organic load, which was twice as high as that with high organic loads. However, SRT had a minor effect on ALE formation. Obviously, such scenarios as starch-rich and low temperature could promote the ALE production. Furthermore, the characteristic analysis including alginate equivalent, different fractions and hydrogel forming property among different ALE, confirmed that the ALE extracted from flocculent sludge had a potential in substituting for commercial alginates. However, different working conditions would exert a significant influence on the composition and chemical properties of ALE, which implies that the controlling some parameters could be an approach to directionally cultivating ALE for their unique structures and potential applications.

Effects of incineration leachate on anaerobic digestion of excess sludge and the related mechanisms

Anaerobic digestion (AD) refers to a reliable channel for energy recovery from organics. However, the digestion efficiency of excess sludge (ES) has been unsatisfactory since there are defects relating to ES hydrolysis. Therefore, this study explored a method to improve the anaerobic digestion of ES, which could simultaneously treat ES and incineration leachate, and revealed the potential mechanism of AD process. As the investigation was conducted on the influences exerted by incineration leachate on the four phases (i.e., solubilization, methanogenesis, acidogenesis and hydrolysis) of ES anaerobic digestion, and the effect mechanism. According to obtained results, adding appropriate amounts of incineration leachate could facilitate the steps of solubilization, hydrolysis, acidogenesis and methanogenesis of ES. The hydrolysis and acidogenesis efficiency in the leachate added digesters were 5.7%–17.1% and 13%–45% higher than that of the control digester, respectively. Meanwhile, cumulative methane yields (CMY) were 27–86 mL/gVS higher than that in the control digester. Besides, the sludge floc stability was reduced by the leachate with the decrease in the median particle size (MPS) and apparent activation energy (AAE) of the sludge. According to microbial community and diversity analysis, adding incineration leachate increased the relative abundance of hydrolytic-acidification bacteria in the digesters and the relative abundance of Methanosaeta and Methanosarcina. Thus, the digestive performance exhibited by the leachate participated system was improved. These mentioned findings may provide an approach for treating ES and incineration leachate in practical engineering.

Performance assessment of ultrasonic sludge disintegration in activated sludge wastewater treatment plants under nutrient-deficient conditions

Although biological oxidation is a commonly applied technique for the removal of pollutants in industrial and municipal wastewater, one major drawback is its excess sludge production, having both an environmental and economic impact. The integration of ultrasonic sludge disintegration in a conventional biological wastewater treatment plant was explored experimentally via assessing the long-term effects on excess sludge reduction by conducting on-site pilot tests at a food processing company and a biodiesel production plant. Two sequencing batch reactors, each with a maximum active volume of 700 L, were operated in parallel for the treatment of industrial wastewater with nutrient deficient characteristics (COD/N/P ratio of 100/1.4/0.12) for over 6 months. One of the reactors was equipped with a side-stream recirculation system to enable the ultrasonic treatment of part of the settled sludge, whereas the other was operated in a conventional way as a reference. The experimental results show a reduction of the observed sludge production yield by 15% to 45% for the ultrasonically treated sequencing batch reactor compared to the conventional one, at a relatively low specific energy of less than 6,000 kJ/kg DS when 15 to 30% of the total sludge mass is treated per day. It was proven that the sludge reduction efficiency is directly proportional to the applied sludge retention time, suggesting that the ultrasonic treatment converts part of the hardly biodegradable particulate material in the activated sludge and improves its biodegradability. During the long-term pilot experiment at the biodiesel production plant, the electrical energy needed for decreasing the excess sludge production by 1 ton could be reduced by more than 80% when the sludge retention time was increased from 11 to 44 days. In addition, the sludge settling characteristics at the food processing company were considerably improved by the ultrasonic treatment, enabling to reduce or even avoid the need for external addition of expensive nutrients to prevent sludge bulking. Finally, an improved effluent quality was observed. Improvements of 7 to 17%, 9 to 20% and 17 to 30% for COD, nitrogen and phosphorus removal, respectively, were established.

Formation, characteristics and control of sludge in Al-containing magnesium alloys: An overview

Sludge consisting of heavy element phases and oxides is often generated during the casting operation of aluminum (Al) and magnesium (Mg) alloys. With the help of the well-established Sludge Factor (SF) formula, it is relatively easy to control the sludge generation in aluminum alloys. But formation mechanisms and characteristics of sludge in die casting magnesium alloys are still unclear. To ensure the production of high quality die cast components at a low cost, a full understanding of sludge in die casting Mg alloys and its proper control measures need to be developed, since excessive sludge formation affects deleteriously material and operation cost, and casting performance. In the present report, the formation, characteristics and control of Mg die-casting sludge, based on the established knowledge of sludge formation and sludge factor in Al die casting alloys, are reviewed. Previous work on characterization and assessment of sludge in die cast Mg alloys are reviewed. Metallurgical principles for control of sludge in ingot production in association with die casting of Mg alloys are discussed. Rapid assessment of Mg oxide and intermetallics relevant to sludge formation in Mg alloys are highlighted.

The Development of the Membrane-Filter Press System(MFPS) by Utilizing Ultrasonic Waves for Treating Sewage Sludge

Sewage treatment plants produce large amounts of sewage sludge yearly in Korea. In this study, a Membrane-Filter Press System (MFPS) using ultrasonic waves was developed to treat sewage sludge at the Seonam sewage treatment plant in Seoul. The MFPS consists of an ultrasonic extractor, a polymer injection tank, a membrane-filter press, and a centrate tank for improving sludge dewatering and phosphorus recovery. Two types of sewage sludge were used: digested raw sludge and digested excess sludge. In lab-scale experiments with an ultrasonic extractor, the concentration of phosphorus was 214.9 mg/L at 50 rpm after sonication at 500 W for 20 min, which was around 4.9 times higher than non-treated sludge. In the pilot-scale experiment, dewaterability of the digested raw and excess sewage sludge was investigated in the MFPS under three sets of operating conditions involving modifier injection, ultrasonication, and polymer injection. it was found that the moisture content of the dewatered digested raw and excess sewage sludge cakes was reduced to 50.5% and 54.3%, respectively. Lowering the moisture content reduced the total volume of the sludge by approximately 40% compared to a conventional centrifugal dehydrator. It is expected that the MFPS will reduce the disposal cost of sludge and offers a sustainable solution for recycling resources.

Feasibility of vermicomposting combined with room drying for enhancing the stabilization efficiency of dewatered sludge

Vermicomposting is characterized by transforming organic waste into nutrient-rich organic fertilizer through the action of different earthworms and microorganisms. Although vermicomposting can recycle the excess sludge in an eco-friendly manner, the longer stabilization period has limited its industrial application. The present study sought to investigate a novel operation process of vermicomposting combined with room drying (VD) to improve the stabilization efficiency of dewatered sludge. Subsequently, the performance and efficiency of vermicomposting without room drying, room dry without vermicomposting, and VD for sludge stabilization were compared simultaneously. In the VD process, the sludge water content reduced from 60.8% to 1.64%, showing the highest electrical conductivity and lowest organic matter content, making the humus substances abundant in the final product. Moreover, the vermicomposting achieved the highest ammonia and nitrate content in final product. Additionally, the bacterial and eukaryotic abundances in the VD product were significantly higher (P < 0.01, i.e., 15.6% and 180.7%) than the vermicomposting product. The specific bacterial genus of Glutamicibacter, Chitinibacter, and Acidobacteria was dominated in the VD product. The Partial least squares-Path modeling (PLS-PM) results revealed that the maturity degree in the VD product was significantly associated with microbial component, and the organic form was strongly driven by the change in the physicochemical properties, which was contradictory to vermicomposting model. The study suggests that the VD process could shorten the vermicomposting period by rapidly accelerating the physical, chemical, and biological stabilization of sludge.

An enhanced excess sludge fermentation process by anthraquinone-2-sulfonate as electron shuttles for the biorefinery of zero-carbon hydrogen

Excess sludge (ES) largely produced in municipal wastewater treatment plants is known as a waste biomass and the traditional treatment processes such as landfill and incineration are considered as unsustainable due to the negative environmental impact. Fermentation process of ES for the biorefinery of zero-carbon hydrogen has attracted an increasing interesting and was extensively researched in the last decades. However, the technology is far from commercial application due to the insufficient effectivity. In the present study, anthraquinone-2-sulfonate (AQS) as electron shuttles was introduced into the fermentation process of ES for mediating the composition and activity of bacterial community to get an enhanced biohydrogen production. Inoculated with the same anaerobic activated sludge of 1.12 gVSS/L, a series of batch anaerobic fermentation systems with various dosage of AQS were conducted at the same ES load of 2.75 gVSS/L, initial pH 6.5 and 35 °C. The results showed that the fermentation process was remarkably enhanced by the introduction of 100 mg/L AQS, accompanying the lag phase was shortened to 1.35 h from 7.62. The obtained biohydrogen yield and the specific biohydrogen production rate were also remarkably enhanced to 24.9 mL/gVSS and 0.3 mL/(gVSS·h), respectively. Illumina Miseq sequencing showed that Longilinea and Guggenheimella as the dominant genera had been enriched from 9.2% to 0–12.0% and 4.7%, respectively, in the presence of 100 mg/L AQS. Function predicted analysis suggested that the presence of AQS had increased the abundance of genes involved in the transport and metabolism of carbohydrate, amino acid and energy production. Further redundancy analysis (RDA) revealed that the enhanced hydrogen production was highly positively correlated with the enrichment of genera such as Longilinea and Guggenheimella. The research work presents a novel potential biorefinery of ES for the effective production of zero-carbon hydrogen.

A Comparison of Biosolids Production and System Efficiency between Activated Sludge, Moving Bed Biofilm Reactor, and Sequencing Batch Moving Bed Biofilm Reactor in the Dairy Wastewater Treatment

Dairy industry wastewater is rich in organic content, presenting a high biodegradability, and therefore biological treatments are widely employed. This study aimed to evaluate biosolids production in three systems: activated sludge (AS), movingbed biofilm reactor (MBBR), and sequencingbatch movingbed biofilm reactor (SBMBBR). Simulated dairy wastewater was used at different organic load rates (OLRs): 1.22, 2.87, and 5.44 gCOD L−1d−1. Besides biosolids production, COD, total carbon (TC), and total nitrogen (TN) removal efficiency was evaluated. Biosolids production was measured in the mixed liquor, carrier-adhered biomass, treated wastewater, and surplus sludge. The operational conditions were kept similar for the three systems, with a carrier filling ratio of 50% for MBBR and SBMBBR. The SBMBBR proved to have better performance in the removal efficiencies of COD, TC, and TN for all OLRs studied. The MBBR presented a similar COD and TC removal efficiency as the SBBR for the two highest OLRs (2.87 and 5.44 gCOD L−1d−1). Concerning biosolids production, the MBBR system produced less biomass and delivered the lowest amount of adhered biomass inside the carriers. The AS treatment generated the highest amount of sludge and offered the worst treatment capability for all OLRs evaluated.

Dual Effect of Acetic Acid Efficiently Enhances Sludge-Based Biochar to Recover Uranium From Aqueous Solution.

Excess sludge (ES) treatment and that related to the uranium recovery from uranium-containing wastewater (UCW) are two hot topics in the field of environmental engineering. Sludge-based biochar (SBB) prepared from ES was used to recover uranium from UCW. Excellent effects were achieved when SBB was modified by acetic acid. Compared with SBB, acetic acid-modified SBB (ASBB) has shown three characteristics deserving interest: 1) high sorption efficiency, in which the sorption ratio of U(VI) was increased by as high as 35.0%; 2) fast sorption rate, as the equilibrium could be achieved within 5.0 min; 3) satisfied sorption/desorption behavior; as a matter of fact, the sorption rate of U(VI) could still be maintained at 93.0% during the test cycles. In addition, based on the test conditions and various characterization results, it emerged as a dual effect of acetic acid on the surface of SBB, i.e., to increase the porosity and add (−COOH) groups. It was revealed that U(VI) and −COO− combined in the surface aperture of ASBB via single-dentate coordination. Altogether, a new utilization mode for SBB is here proposed, as a means of efficient uranium sorption from UCW.

The occurrence and removal of steroid estrogens in a full-scale anaerobic/anoxic/aerobic-membrane bioreactor process and the implication of the bacterial community dynamics

The occurrence and removal of estrone (E1), 17β-estradiol (E2), and 17α-ethinylestradiol (EE2) as typical steroid estrogens (SEs) and the bacterial community structure in a full-scale anaerobic/anoxic/aerobic-membrane bioreactor (A2O-MBR) process were investigated. Residual E1 and EE2 were detected in the effluent, while the excess sludge remained all types of SEs. The biodegradation of SEs occurred primarily in the aerobic tank and the sorption capacity of SEs on activated sludge decreased along the flow course. The internal recirculation ratio applied in the A2O-MBR process failed to form distinct redox conditions. Water temperature was the predominant factor affecting bacterial community composition and SEs biodegradation. Genera not previously reported as SE biodegraders might be responsible for SEs biodegradation in full-scale processes exposed to environmentally relevant SEs concentrations. Heterotrophic cometabolism was inferred as the primary SEs biodegradation mechanism. The present study revealed the correlations between operational factors and SEs biodegradation and the significance of enriching bacterial populations responsible for SEs biodegradation to improve the potential of A2O-MBR process as a SEs barrier.

Minimizing excess sludge production under synergistic effect of diatomite and uncoupling agent 2,4-dinitrophenol: An in-depth study

Excess sludge production is one of the major challenges in the wastewater treatment plants worldwide. The main solution is to reduce the burden of sludge by lowering its production. In this study, the strategies for sludge reduction using uncoupler DNP (2,4-dinitrophenol) with diatomite or diatomaceous earth (natural sedimentary rock) are evaluated for practical application using cost analysis and assessment of environmental impact. There was a decrease in average removal efficiency of chemical oxygen demand (COD), ammonia nitrogen (NH 4 + -N) and total nitrogen (TN) of 7–30%, 20% and 44%, respectively. The sludge volume index (SVI) was 80–120 mL/g while the sludge activity increased by 21%. By cost analysis and comparison of the various parameters, it was determined that the optimal dosage of DNP was 6 mg/L. The problem of poor effluent quality and sludge performance caused by the addition of DNP alone was solved by the collaborative addition of DNP and diatomite. Diatomite can absorb the coupling agent like a carrier to form a compound uncoupling agent. Diatomite easily aggregate and mixed with sludge micelle particles. DNP will slowly release and dissolve into sludge micelles after they are mixed, resulting in higher DNP concentration in sludge micelles. A synergistic effect of DNP and diatomite on sludge reduction showed increase in removal efficiency COD, NH 4 + -N and TN of 13.35%, 18.6% and 26.58%, respectively. SVI was decreased by 13%. A sewage treatment of 1 m 3 can still save sludge treatment cost by $ 0.0084. Comparing the synergistic dose, observed sludge yields (Yobs) decreased by 28.28% (48 mg of DNP with 0.4 g of diatomite; one-time dosage per two-days) and 21% (24 mg of DNP with 0.2 g of diatomite; once a day dosage). The sludge activity also increased. By orthogonal test results, the optimum environmental influence factors for the treatment system are set to 25 °C and pH 7.

Full-scale application of a down-flow hanging sponge reactor combined with a primary sedimentation basin for domestic sewage treatment.

The down-flow hanging sponge (DHS) reactor is advantageous for sewage treatment since it produces an effluent quality that complies with the standards for reuse and there is little excess sludge. A full-scale DHS module was efficiently employed for the treatment of domestic sewage (200 m3day-1) flowing from a primary sedimentation basin (PSB), which was used to reduce the suspended solids loading rate and enhance the oxidation of organics by heterotrophs. The combined PSB-DHS was successfully operated at a total hydraulic retention time of 3.4h (2.4h for PSB and 1.0h for DHS) for the relatively long period of 600days at sewage temperatures of 10°C to 32°C. The PSB-DHS consistently produced an effluent quality with minimum values of chemical oxygen demand, biochemical oxygen demand, and suspended solids of 59 ± 15, 12 ± 3.0, and 15 ± 7mg L-1, respectively. The proposed system performed exceptionally well at removing organics and particulate matter over a short hydraulic retention time.

Understanding the mechanism of polybrominated diphenyl ethers reducing the anaerobic co-digestion efficiency of excess sludge and kitchen waste.

Polybrominated diphenyl ethers (PBDEs) widely existing in the environment can pose a serious threat to the ecological safety. However, the influence of PBDEs on methane production by excess sludge (ES) and kitchen waste (KW) anaerobic co-digestion and its mechanism is not clear. To fill this gap, in this work, the co-digestion characteristics of ES and KW exposed to different levels of PBDEs at medium temperature were investigated in sequencing batch reactor, and the related mechanisms were also revealed. The results showed that PBDEs reduced methane production and the proportion of methane in the biogas. Methane yield decreased from 215.3mL/g· volatile suspended solids (VSS) to 161.5mL/(g·VSS), accompanied by the increase of PBDE content from 0 to 8.0mg/Kg. Volatile fatty acid (VFA) yield was also inhibited by PBDEs; especially when PBDEs were 8.0mg/Kg, VFA production was only 215.6mg/g VSS, accounting for 75.7% of that in the control. Mechanism investigation revealed PBDEs significantly inhibited the processes of hydrolysis, acidogenesis, acetogenesis, and methanogenesis. Further study showed that PBDEs could inhibit the degradation and bioavailability of ES and KW, but it had a greater inhibition on the utilization of KW. Enzyme activity investigation revealed that all the key enzyme activities related to methane production were suppressed by PBDEs.

Recovering double-metal hydroxides precipitate from desalination process of saline wastewater as conditioner for excess sludge dewatering

The massively generated double-metal hydroxides (DHs) precipitate has restricted the application of the lime-aluminum precipitation method in the zero liquid discharge (ZLD) process of saline wastewater. Recovering DHs precipitate as conditioners for the dewatering of municipal sludge is a promising solution for above issue. In this study, individual use of DHs from the ZLD process, including ettringite (Ett), Friedel’s salt (FS) and their mixtures (EF), and combined use of the DHs and FeCl3 in sludge conditioning were investigated. The EF precipitate was commonly generated from the chloride precipitation process by the lime-aluminum method, and composed of 16.7% of Ett and 83.3% of FS. The dewaterability of excess sludge conditioned with FeCl3 prior to DHs was much better than opposite dosing sequence and individual use of DHs. Sludge conditioned by FeCl3 prior to EF possessed the best dewatering performance ascribing to its high fluidity, strong structure strength and uniformly dispersed mesoporous structure. The variations of extracellular polymeric substances (EPS) further confirmed that EPS were largely released after FeCl3 addition and then efficiently adsorbed by the subsequently added DHs, with the highest adsorption efficiency of 60% by EF. The kinetics for EPS adsorption also suggested that EF had the highest adsorption capacity compared to FS and Ett. Overall, FeCl3 addition could form interstitial channels in flocs by penetration and release external and intracellular substances, while the latter added EF, Ett could function as uniformly skeleton material and dispersing agent to improve EPS adsorption by FS. Hence, the synergic coupling of FeCl3 and DHs as chemical conditioner is inspirable and economically beneficial to ZLD and advanced sludge dewatering process.

A Low Cost Fe3O4-Activated Biochar Electrode Sensor by Resource Utilization of Excess Sludge for Detecting Tetrabromobisphenol A.

Owing to its ubiquity in natural water systems and the high toxicity of its accumulation in the human body, it is essential to develop simple and low-cost electrochemical sensors for the determination of 3,3′,5,5′-tetrabromobisphenol A (TBBPA). In this work, Fe3O4–activated biochar, which is based on excess sludge, was prepared and characterized using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR) and BET analysis to analyze its basic features. Subsequently, it was used to fabricate an electrochemical sensor for the detection of TBBPA. The electrochemical test results revealed that the Fe3O4–activated biochar film exhibited a larger active surface area, a lower charge transfer resistance and a higher accumulation efficiency toward TBBPA. Consequently, the peak current of TBBPA was significantly enhanced on the surface of the Fe3O4–activated biochar. The TBBPA sensing platform developed using the Fe3O4–activated biochar composite film, with relatively a lower detection limit (3.2 nM) and a wider linear range (5–1000 nM), was successfully utilized to determine TBBPA levels in water samples. In summary, the effective application of Fe3O4–activated biochar provided eco-friendly and sustainable materials for the development of a desirable high-sensitivity sensor for TBBPA detection.

Explore the closed-loop disposal route of surplus sludge: Sludge self-circulation preparation of sludge-based biochar (SBB) to enhance sludge dewaterability

Sludge-based biochar (SBB) has been used to improve excess sludge dewaterability. However, the conditionings of sludge dewaterability using SBB prepared by different methods are discrepant. Herein three SBBs (SBB0, SBB1, SBB2) were prepared by direct carbonization, ZnCl2 pre-activation and carbonization-HCl post-activation method respectively.The feasibility of SBB as sludge dewatering conditioner and the mechanism were mainly explored. The results demonstrated that all three SBBs enhance sludge dewatering. SBB1 had the best conditioning effect among all the three methods at the same dosage. SBB particles significantly reduced the compressibility of sludge and improved the porosity of sludge cake. Zeta potential analysis showed that the positive charge on the surface of SBB could neutralize the sludge flocs with negative charges, reduce the electrostatic repulsion between sludge particles, make the sludge destabilize and aggregate. The SBB characteristics exhibited a coagulant aid effect. Meanwhile, SBB promotes the dissolution of inner EPS and effectively weakens the water holding capacity of sludge flocs by adsorbing viscous macromolecules through non-covalent interactions. Sludge colloid destabilization, EPS dissolution and removal of water-holding substances played a synergistic effect in the process of weakening the affinity between water molecules and solid phase. The specific surface area, pore volume, the number and type of surface functional groups, the content of silicon and aluminum compounds of SBB1 were better than those of SBB0 and SBB2 combined with the characterization results of three SBBs.Therefore SBB1 had the best effect on sludge dewatering. The proposed closed-loop sludge disposal route by sludge self-circulation using SBB derived from wastewater treatment plants (WWTPs) is a green sustainable insight and a promising research direction.

Application of Natural Coagulants for Pharmaceutical Removal from Water and Wastewater: A Review

Pharmaceutical contamination threatens both humans and the environment, and several technologies have been adapted for the removal of pharmaceuticals. The coagulation-flocculation process demonstrates a feasible solution for pharmaceutical removal. However, the chemical coagulation process has its drawbacks, such as excessive and toxic sludge production and high production cost. To overcome these shortcomings, the feasibility of natural-based coagulants, due to their biodegradability, safety, and availability, has been investigated by several researchers. This review presented the recent advances of using natural coagulants for pharmaceutical compound removal from aqueous solutions. The main mechanisms of natural coagulants for pharmaceutical removal from water and wastewater are charge neutralization and polymer bridges. Natural coagulants extracted from plants are more commonly investigated than those extracted from animals due to their affordability. Natural coagulants are competitive in terms of their performance and environmental sustainability. Developing a reliable extraction method is required, and therefore further investigation is essential to obtain a complete insight regarding the performance and the effect of environmental factors during pharmaceutical removal by natural coagulants. Finally, the indirect application of natural coagulants is an essential step for implementing green water and wastewater treatment technologies.

Occurrence, distribution and removal of polycyclic aromatic hydrocarbons in a typical process for textile wastewater treatment of the Pearl River Delta Region, South China

This investigation aimed at revealing the occurrence, distribution and removal of polycyclic aromatic hydrocarbons (PAHs) in a typical process for textile wastewater treatment of the Pearl River Delta Region, South China. The results demonstrated that 16 PAHs were all measured in the dissolved and adsorbed state excepting acenaphthylene in suspended solids. In the influent, the total PAHs ranged from 1210.18 to 1304.93 ng/L in the dissolved state, and the PAHs with 2 and 3 rings were the predominant, accounting for 83.78 ± 3.66%, while, in the adsorbed state, it ranged from 2152.54 to 2554.18 ng/g, and the PAHs with 3 and 4 rings were the most abundant, accounting for 89.41 ± 5.31%. The removal efficiencies of dissolved individual PAHs ranged from 81.38% to 100% in the whole treatment process, in which, PAHs with low molecular weight achieved higher removal efficiency in the anaerobic digestion step, and PAHs with high molecular weight (HMW) were easier to be removed in the sedimentation step. Such results verified that the number of benzene ring in PAHs was closely related to their occurrence, distribution and removal, and a risk assessment indicated that the HMW PAHs accumulated in the sedimentation tank might increase the environmental risk of excess sludge.

UASB Performance and Perspectives in Urban Wastewater Treatment at Sub-Mesophilic Operating Temperature

UASBs present several advantages compared to conventional wastewater treatment processes, including relatively low construction cost facilities, low excess sludge production, plain operation and maintenance, energy generation in the form of biogas, robustness in terms of COD removal efficiency, pH stability, and recovery time. Although anaerobic treatment is possible at every temperature, colder climates lead to lower process performance and biogas production. These factors can be critical in determining the applicability and sustainability of this technology for the treatment of urban wastewater at low operating temperature. The purpose of this study is the performance evaluation of a pilot-scale (2.75 m3) UASB reactor for treatment of urban wastewater at sub-mesophilic temperature (25 °C), below the optimal range for the process, as related to biogas production and organic matter removal. The results show that, despite lower methane production and COD removal efficiency compared to operation under ideal conditions, a UASB can still achieve satisfactory performance, and although not sufficient to grant effluent discharge requirements, it may be used as a pretreatment step for carbon removal with some degree of energy recovery. Options for UASB pretreatment applications in municipal WWTPs are discussed.