•GAC addition led to higher COD removal and methane production.•GAC addition modified the relation between methanogens and SRB.•GAC enriched Geobacter, Syntrophus, SRB and Methanobacterium.•GAC ...showed a protective effect on methanogens under sulfate-reducing conditions.
Two laboratory-scale up-flow anaerobic sludge blankets (UASB) reactors treating municipal sewage were operated to test the effects of granular activated carbon (GAC) addition under sulfate-reducing and psychrophilic conditions. As compared to the non-GAC reactor, the GAC-amended reactor simultaneously enhanced chemical oxygen demand (COD) removal (from 61% to 69%) and methane production (from 11% to 20%) (all with P < 0.05). With a stepwise decrease in the hydraulic retention times, the specific methanogenic activity (SMA) using acetate as substrates decreased in both reactors (from 30 to 24 and 66 to 48 mg CH4-COD/g VSS/d, in the non-GAC and GAC-amended UASB, respectively); whereas SMA using hydrogen as substrates decreased in the non-GAC UASB (from 42 to 31 mg CH4-COD/g VSS/d), and increased in the GAC-amended UASB (from 58 to 89 mg CH4-COD/g VSS/d). Microbial community analysis revealed that Geobacter was enriched in the GAC-biofilm (4.9%), higher than that in the suspended sludge of the non-GAC UASB (0.7%) and GAC-amended UASB (1.4%) at the end of the operation. Methanobacterium, Syntrophus, and sulfate-reducing bacteria were also enriched in the GAC-amended UASB. Our results indicate that GAC may stimulate potential bio-electric active microorganisms, resulted in enhancing methanogenesis during anaerobic digestion of municipal sewage.
•Soxhlet extraction of lipids from municipal sewage sludge using methanol as a solvent.•Kinetics and thermodynamics modeling of lipids extraction from municipal sewage sludge.•Synthesis of biodiesel ...from municipal sewage sludge lipids with catalytic transesterification process.
Safe disposal of municipal sewage sludge is a severe environmental issue in the wastewater treatment plan worldwide due to its enormous volume of generation and containing hazardous substances. The purpose of the present study is to appraise the possibility of utilizing the municipal sewage sludge as a lipids feedstock for biodiesel production. Lipids from the municipal sewage sludge were extracted via the soxhlet extraction method using methanol as a solvent. The soxhlet extraction of lipids was conducted with varying temperature (40–80 °C), treatment time (2–12 h), and sewage sludge to solvent (S/L) rato (1: 05–1:10). The maximum lipids extraction obtained about 27% from municipal sewage sludge using methanol as a solvent at S/L ratio of 1: 10, the temperature of 70 °C, and a treatment time of 8 h. Thermodynamics and kinetics behavior of the soxhlet extraction of lipids were determined using Eyring theory and a second-order rate equation, respectively. Approximately 84% of biodiesel was synthesized from soxhlet extracted lipids using the alkaline transesterification method at a catalyst loading of 5 wt%, temperature of 60 °C, an oil and methanol molar ratio of 1:9, and reaction time of 4 h. The physicochemical characterization of biodiesel showed that the biodiesel properties complied with the American Society for Testing and Materials standards of D6751 (ASTM D6751) and European Nationals standards of 14214 (EN 14214). The finding of the present study showed that the municipal sewage sludge could be consumed as an impending feedstock for biodiesel production.
In recent years, a sharp increase in the amount of municipal sewage sludge (MSS) in Tibet has posed serious threats to the fragile ecological environment. Tibetan sludge, with a high content of ...volatile and low heavy metals, has re-utilization advantages, and thus, the selection of appropriate utilization processes for Tibetan MSS is of great importance. In this study, not only the processes themselves, but also other factors including legislations and environmental pollution were investigated. This study introduced the current waste management legislation situation (especially for MSS) in China and Tibet, China. Moreover, a series of SWOT (strength & weakness and opportunity & threats) analyses were conducted to compare anaerobic digestion (AD), incineration, pyrolysis (PY), gasification, and anaerobic digestion coupled with pyrolysis. The results showed that anaerobic digestion coupled with pyrolysis was the optimal treatment option, because anaerobic digestion was suitable for the low oxygen content in Tibet. Although only 50–60% of the organic matter in MSS could be degraded by anaerobic digestion, the residual organic matter (energy) could be further decomposed by pyrolysis, converting it into pyrolytic gas, bio-oil, and biochar, as valuable products. Sludge digestate pyrolysis could reduce environmental risks, save energy, recover materials, and produce high value-added materials. Moreover, it provides a “zero waste” solution for sludge disposal and promotes a “Circular Economy.” The challenges and obstacles of MSS anaerobic digestion coupled with pyrolysis in Tibet were also investigated. This study provides an important technical reference for the comprehensive utilization of Tibetan MSS.
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•The sharp increase of MSS in Tibet emphasizes the necessary of MSS management.•Tibetan MSS shows advantages for re-utilization.•5 MSS re-utilization processes were evaluated by SWOT analysis.•AD coupled with PY process has great potential in MSS re-utilization in Tibet.•The challenges and recommendations of coupled process in Tibet were investigated.
•Municipal sewage sludge was pyrolyzed at various temperature.•Pyrolysis temperature influences the properties of biochar strongly.•Biochars perform better than commercial activated carbon on heavy ...metal adsorption.•The purpose of both energy recovery and heavy metal removal can achieve at 900°C.
To investigate systematically the influence of pyrolysis temperature on properties and heavy metal adsorption potential of municipal sludge biochar, biophysical dried sludge was pyrolyzed under temperature varying from 500°C to 900°C. The biochar yield decreased with the increase in pyrolysis temperature, while the ash content retained mostly, thus transforming the biochars into alkaline. The structure became porous as the temperature increased, and the concentrations of surface functional group elements remained low. Despite the comparatively high content of heavy metal in the biochar, the leaching toxicity of biochars was no more than 20% of the Chinese standard. In the batch experiments of cadmium(II) adsorption, the removal capacity of biochars improved under higher temperature, especially at 800°C and 900°C even one order of magnitude higher than that of the commercial activated carbon. For both energy recovery and heavy metal removal, the optimal pyrolysis temperature is 900°C.
•The MSS co-combustion modes in full scale coal-fired power plants are introduced.•The heavy metals content in ash and slag did not exceed the risk screening value.•Heavy metals showed significant ...enrichment in the ash and dilution in the slag.•The leaching concentrations of Cr and Ni were several times the limit value.•Cr and Hg were the major contributors to potential ecological risks of slag and ash.
Co-combustion in coal-fired power plants is one of the main methods to dispose of municipal sewage sludge (MSS). The high heavy metals content of MSS increases the ecological risk of ash from the coal and MSS co-combustion. In response to this problem, the three types of fly ash or bottom ash from MSS co-combustion in the three coal-fired power plants were sampled. The properties of fly ash and bottom ash were analyzed in terms of ash composition, particle size distribution, heavy metals content and leaching characteristics. The potential ecological risks were evaluated using the ecological risk index assessment method. The results showed that the co-combustion of MSS had no significant effect on the ash composition order and heavy metals content order. However, the total content of Cu, Mn, Pb and Zn, Hg in the co-combustion ash was higher than that in the coal-fired ash without sludge blending but did not exceed the risk screening value for soil heavy metal contamination of residential land. Heavy metals showed significant enrichment in fly ash and dilution in bottom ash. The leaching concentrations of Cr and Ni were several times the limit value. The potential ecological risk levels of fly ash and bottom ash were moderate risk and high risk respectively. Cr and Hg were the main contributors to potential ecological risks. The contents of Cr, Hg and Ni need to be paid attention to in the subsequent utilization of coal ash mixed with co-combustion of sewage sludge.
Hydrothermal Liquefaction (HTL) could be a promising and better alternative to other techniques for energy recovery from municipal sewage sludge (MSS). However, the nutrients (i.e., N, and P) ...recovery potential from the byproducts, generated in the HTL of MSS, needs to be studied so that a comprehensive sludge management practice could be adopted. In this study, HTL process temperature (275–400 °C), and reaction time (30–120 min) were first investigated for biocrude yield and release of the nutrients to the aqueous phase liquid (APL) and biochar. The maximum energy recovery (i.e., 59%) and maximum energy return on investment (i.e., 3.5) were obtained at 350 °C and 60 min of holding time. With the increase in HTL reaction time, the concentration of nitrogen in the APL increased (5.1 to 6.8 mg/L) while the concentration of phosphorus decreased (0.89 to 0.22 mg/L); the opposite was observed for the biochar. The nutrient recycling efficiency from the APL using microalgae was found to be strain-specific; nitrogen recycling efficiency by Picochlorum sp. and Chlorella sp. were 95.4 and 58.6%, respectively. The APL, derived from 1 kg MSS, could potentially produce 0.49 kg microalgal biomass. Since the concentrations of various metals in the biochar samples were substantially lower compared to their concentrations in raw MSS, the application of biochar as a soil conditioner could be very promising. Overall, net positive energy could be recovered from MSS using the HTL process, while the nutrients in the APL could be used to cultivate specific microalgae, and biochar could be applied to enhance the soil quality.
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•Optimal HTL conditions could recover 58% energy of the MSS with a EROI value of 3.5.•Increasing HTL reaction time reduced the TOC and increased TN in APL.•Metals concentrations in the biochar get reduced compared to raw MSS.•TP in the biochar increased with increase in HTL reaction time.•Microalgal recycling efficiency of the nutrients from the APL was strain dependent.
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•PN/A-EPD/A process was developed in an IFAS-SBR treating real municipal wastewater.•High NRE of 90.1% was achieved under aerobic HRT of 8 h and DO of 0.4 ± 0.1 mg/L.•89.9% of TN was ...removed by anammox pathway in typical cycle.•Relative abundance of Candidatus Brocadia rose from 0% to 0.79% in suspended sludge.
In this study, an innovative partial nitrification-anammox (PN/A) and endogenous partial denitrification-anammox (EPD/A) process was developed in a single-stage integrated fixed film activated sludge sequencing batch reactor (IFAS-SBR) treating real municipal wastewater with C/N ratio below 3.2. Enhanced efficiency of total nitrogen (TN) removal reached 90.1% with low HRT of 12 h and DO of 0.4 ± 0.1 mg/L. Detailed nitrogen removal mechanism analysis of typical cycle revealed that 89.9% of TN was eliminated through anammox pathway. Anammox bacteria (Candidatus Brocadia) and endogenous denitrifying bacteria (Candidatus Competibacter) were abundant both in biofilms and suspended sludge, meanwhile ammonium-oxidizing bacteria has outcompeted nitrite-oxidizing bacteria, which all favored the synergistic effect of anammox with PN and EPD and contributed to the improvement of nitrogen removal. Overall, the above results confirmed that combined PN/A and EPD/A process is a reliable and efficient alternative for mainstream anammox process.
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•Effect of different pretreatments of industrial FW and WSS was investigated on AD.•US-AL hybrid pretreatment improved degradation of sCOD, carbohydrate, and protein.•Strong ...acid-alkali and thermal pretreatment reduced biogas and methane production.•Methane yield improved by 49% by US-AL hybrid pretreatment.•Kinetic models were applied for cumulative biogas productions of selected mixtures.
This study presents the effect of mechanical, chemical, thermal, and hybrid pretreatment on anaerobic digestion of fruit-juice industrial waste (FW) co-digested with municipal sewage sludge (MSS). The pretreatment of the substrates with ultrasonication, microwave, weak alkali-acid caused an increase in cumulative biogas production of approximately 20.9, 14.9, 8.1, and 5.2%, respectively. Beside this, thermal and strong acid-alkali pretreatment reduced biogas production. The highest cumulative biogas and methane yield was increased with hybrid pretreatment which contains ultrasonication (US) and alkali (AL) pretreatment by 36% and 49%, respectively. Also, compared to untreated mixture, the soluble COD, carbohydrate, and protein removal efficiencies were increased from 42.6% to 65.6%, 65.1% to 86.6%, and 17.3% to 62.4%, respectively for US-AL pretreatment. The kinetic parameters of cumulative biogas production for the selected reactors were further estimated with Monod, Cone, and Transference Function models.
A series of hydrothermal liquefaction (HTL) experiments with two different samples of municipal sewage sludge (MSS) were conducted at 350 °C for 30 min residence time in a high pressure batch ...reactor. The main aim of the study was to explore the distribution and migration pathways of a broad range of metals and metalloids in the HTL products (bio-oil, char and aqueous phase) obtained in the presence of various homogeneous and heterogeneous catalysts (Na2CO3, Li2CO3, K2CO3, Ba(OH)2, Fe2O3, CeO2, NiMo/MoO3, MoS2, Ni/NiO, SnO2, FeS). The elements under study included 16 environmentally significant metals and metalloids (As, B, Ba, Cd, Co, Cr, Cu, Mn, Mo, Ni, Pb, Sb, Se, Sn, Zn and Hg). The study showed that the quantitative migration of the tested metals and metalloids to the particular HTL products, relative to their initial content in the raw sludge, is different for the individual elements. Most metals exhibited a particularly strong affinity to the solid fraction (biochar). In the obtained HTL bio-oils, all tested elements were identified, except of Cd. It was also found that B and As have high affinity to the aqueous phase. A direct effect of catalysts on the contents of some elements in the products was also proved by the study, e.g. increased concentration of Cr in the biochar when Fe2O3 was used as a process catalyst. Due to the wide scope of the tested elements and broad range of catalyst used, the results obtained represent a unique and comprehensive set of environmental data compared to similar HTL studies previously conducted for MSS.
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•Sewage sludge hydrothermal liquefaction with various catalysts was performed.•The behavior of 16 metals and metalloids in HTL products was discussed.•A particularly strong affinity of the tested elements to the biochar was observed.•Inorganic matter in sewage sludge increases the metal content in HTL products.•Metals present in catalysts (e.g. Ba, Ni, Mo) migrate to HTL biochar and bio-oil.
This study provides a feasible scheme for the treatment of municipal sewage through simultaneous partial nitritation, anammox, and denitrification (SNAD) process, which was realized in a single-stage ...biofilter reactor (BFR). First, the BFR was started up to enrich the anaerobic ammonium-oxidizing bacteria (AnAOB) in the upper part of the reactor through the operation mode of the top influent and bottom effluent. Then, the BFR was inoculated with activated sludge and aerated continuously at the bottom to realize the coupling of SNAD, which was accompanied by a two-point influent from the bottom and top effluent. Results indicated that the high removal efficiency of NH4+-N (93.40%), total nitrogen (TN, 89.95%), and soluble chemical oxygen demand (SCOD, 92.68%) were achieved with an air–water ratio of 4.29 and hydraulic retention time (HRT) of 6 h. During the SNAD steady phase for the treatment of simulated municipal sewage with a soluble chemical organic demand to nitrogen (C/N) ratio of 2.31, low concentrations of NH4+-N (4.13 mg/L), TN (6.44 mg/L), and SCOD (11.29 mg/L) were attained in the effluent. High-throughput sequencing analysis indicated that the relative abundance of Nitrosomonas, Candidatus Brocadia, and Denitratisoma were 0.77%, 0.43%, and 4.07% in the biofilm at the 0–12.5 cm zone, respectively, suggesting successful implementation of the SNAD process.
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•The treatment of municipal sewage with the single-stage BFR is feasible.•The SNAD process can be realized through start-up from both ends of the BFR.•Two-point influent favored the simultaneous removal of N and SCOD in the BFR.•Exactly 89.95% TN and 92.68% SCOD were removed in BFR under HRT of 6 h.
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