Synergetic Bioproduction of Short-Chain Fatty Acids from Waste Activated Sludge Intensified by the Combined Use of Potassium Ferrate and Biosurfactants

The synergetic effect and underlying mechanism of potassium ferrate(PF)with tea saponin(TS,a biosurfactant)in producing short chain fatty acids(SCFAs)from anaerobic fermentation of waste activated sludge(WAS)were explored in this work.Experimental results showed that 0.2 g PF(g TSS)^(-1)(total suspended solid)combined with 0.02 g TS(g TSS)^(-1) could further improve SCFAs’production,and the maximum SCFAs content reached 2008.7 mg COD L^(-1),which is 1.2 and 4.5 times higher than those with PF and TS individually added,respectively,and 5.3 times higher than that of blank WAS on Day 12.In the model substrates experiments,the degradation rates of bovine serum albumin and dextran with combination of PF and TS were 41.3%±0.1% and 48.5%±0.06%,respectively,on Day 3,which are lower than those in blank WAS(with degradation rates of 72.3%±0.5%and 90.3%±0.3%).It was revealed that the oxidative effect of PF and the solubilization of TS caused more organic matters to be dissolved out from WAS,providing a large number of biodegradable substances for subsequent SCFAs production.While WAS pretreated with the combination of PF and TS,the relative abundances of Firmicutes increased from 6.4%(blank)to 38.6%,and that of Proteobacteria decreased from 41.8%(blank)to 21.8%.The combination of PF and TS promoted the hydrolysis process of WAS by enriching Firmicutes,and then increased acetic acid production by inhibiting Proteobacteria that consumed SCFAs.Meanwhile,at the genus level,acidogenesis bacteria(e.g.,Proteiniclasticum and Petrimonas)were enriched whereas SCFAs consuming bacteria(e.g.,Dokdonella)were inhibited.

Short-process recycling of Nd-Fe-B sintered magnet sludge wastes:Challenges and approaches

Nd-Fe-B sintered magnet sludge wastes are one kind of typical commodity of recyclable rare-earth permanent magnet resources,and recycling such kind of wastes with economical and environmentally friendly techniques is crucial to the sustainable rare-earth industry.However,the current multistage wet process recycling technique for the sludge wastes involves high fabrication cost,excessive energy consumption,and heavy environmental burden.Therefore,short-process recycling techniques for Nd-Fe-B sintered magnet wastes have drawn increasing attention in the past decades.In this paper,we review recent efforts into short-process recycling Nd-Fe-B sintered magnet sludge wastes with emphasis on in-situ recycling techniques.

Effects of Potassium Ferrate and Low-Temperature Thermal Hydrolysis Co-Pretreatment on the Hydrolysis and Anaerobic Digestion Process of Waste Activated Sludge

This study evaluated the effect of potassium ferrate(PF)and low-temperature thermal hydrolysis co-pretreatment on the promotion of sludge hydrolysis process and the impact on acid production in the subsequent anaerobic digestion process.The analytical investigations showed that co-pretreatment significantly facilitated the hydrolysis process of the sludge and contributed to the accumulation of short-chain fatty acids(SCFAs).The pretreatment conditions under the optimal leaching of organic matter from sludge were hydrothermal temperature of 75℃,hydrothermal treatment time of 12 h,and PF dosage of 0.25 g g^(−1)TSS(total suspended solids),according to the results of orthogonal experiments.By pretreatment under proper conditions,the removal rate of soluble chemical oxygen demand(SCOD)achieved 71.8%at the end of fermentation and the removal rate of total phosphorus(TP)was 69.1%.The maximum yield of SCFAs was 750.3 mg L^(−1),7.45 times greater than that of the blank group.Based on the analysis of the anaerobic digestion mechanism,it was indicated that the co-pretreatment could destroy the floc structure on the sludge surface and improve organic matter dissolving,resulting in more soluble organic substances for the acidification process.Furthermore,microbial community research revealed that the main cause of enhanced SCFAs generation was an increase in acidogenic bacteria and a reduction of methanogenic bacteria.

Kinetic analysis of waste activated sludge hydrolysis and short-chain fatty acids production at pH 10

The accumulation of short-chain fatty acids （SCFAs）, a preferred carbon source for enhanced biological phosphorus removal microbes, was significantly improved when waste activated sludge （WAS） was fermented at pH 10. The kinetics of WAS hydrolysis and SCFAs production at pH 10 was investigated. It was observed that during WAS anaerobic fermentation the accumulation of SCFAs was limited by the hydrolysis process, and both the hydrolysis of WAS particulate COD and the accumulation of SCFAs followed first-order kinetics. The hydrolysis and SCFAs accumulation rate constants increased with increasing temperature from 10 to 35℃, which could be described by the Arrhenius equation. The kinetic data further indicated that SCFAs production at pH 10 was a biological process. Compared with the experiment of pH uncontrolled （blank test）, both the rate constants of WAS hydrolysis and SCFAs accumulation at 20℃ were improved significantly when WAS was fermented at pH 10.

Simulation and assessment of sludge concentration and rheology in the process of waste activated sludge treatment

The process of using flat-sheet membrane for simultaneous sludge thickening and digestion （MSTD） was employed. The variations of sludge concentration and rheology were characterized and simulated. Based on mass balance analysis, mathematical models were developed and successfully used to predict and evaluate the variations of sludge concentration and the digestion efficiency in the MSTD process. The apparent viscosity of sludge could be modeled as functions of mixed liquor suspended solids and shear rates. The sludge in the MSTD process showed both shear-thinning and viscoplastic behaviour, and under various shear rates different rheological models could be chosen to predict their flow behaviour. It was also found that sludge concentration and viscosity had significant correlations with membrane fouling in the MSTD process.

Solid- liquid phase separation and resource recycling study for waste rolling oily sludge

On the basis of the characteristics of a highly emulsified solid-liquid phase （fine particles, sticky consistency,black color, and low reuse ratio）, waste rolling oily sludge has been a focal problem in the steel industry. In this article, a solid-liquid phase separation and resource recycling process was described, with pilot test results showing that flocculation-sedimentation is an effective pretreatment, and that the filtration-coagulationvacuum distillation process is simple and feasible with a 53.5% recovery rate for regenerated oil that is qualified for return to the roiling production line. Then,solid phase oil-sludge was extracted by solvents with a 77% metal resource recovery rate and a wide utilization range. Finally, according to the experimental results, a set of feasibility plans for a 50 t/a waste rolling oily sludge solid-liquid separation and resource recycle project was designed, with the expectation of 50% regenerated oil yield, 70% solid metal resource recovery, and a 2. 5-year investment payback period.

Influence of Pore-expansion Agent on the Structure and Performance of Activated Alumina Synthesized from Waste Aluminum Sludge

The chemical compositions of the sludge after treatment are tested by fully chemical analysis techniques. Its crystalline phase structure changes of the sludge calcined at different temperature are characterized by XRD method. Nitrogen gas isothermal adsorption method （77 K） is applied to measure the influences of ammonium bicarbonate on specific surface area and pore structure of activated alumina synthesized from waste aluminum sludge. The result shows that the amount of Al2O3 in the sludge accounts for more than 94%, and Na2Owt% in a 0.1-0.2% range. By calcining raw sludge at 600℃, monophase γ-Al2O3 is obtained. And this can satisfy the performance requirements of activated alumina adsorbent. The specific surface area of the specimen with NH4HCO3 added has expanded from 179 to 249 m^2/g and the pore volume from 0.25 to 1.11 cm^3/g as well as the average pore diameter from 5.6 to 17.8 nm. All these show that NH4HCO3 is an effective pore-expansion agent to remarkably improve the structure and performance of activated alumina synthesized from waste aluminum sludge.

Real-time control of aerobic/anoxic digestion for waste activated sludge

Experiments were conducted to study the performance characters of aerobic/anoxic （A/ A） digestion of sludge at 30± 1 ℃, while the sludge retention time （SRT） was kept 16 d. The varia tions of oxidation reduction potential （Eh ） and pH were continuously monitored during the A/A di gestion and the conversions of ammonium and nitrate were investigated. Important features on both Eh and pH profiles were identified to develop process control strategy. Since the feature point on Eh profile where d2 Eh/dt^2 =0 is very stable during anoxic cycle, it can be used to determine the end of denitrification. The end of nitrification can be identified according to dpH/dt = 0. A real-time control strategy of A/A digestion of sludge was developed and tested with pH and Eh as control parameters. It is shown that the performance of the real-time control strategy is better than that of a fixed time control strategy. While the real time controlled A/A digestion system can achieve a similar volatile suspended solids （VSS） destruction efficiency of 35.2 % as a continuously aerated system, it im proves the supernatant quality in a shorter aeration time（7. 75 d for a 20 d period）.

Microbial Community Profiles Related to Volatile Fatty Acids Production in Mesophilic and Thermophilic Fermentation of Waste Activated Sludge Pretreated by Enzymolysis

Mesophilic and thermophilic anaerobic fermentation performance of waste activated sludge(WAS)pretreated by enzymes catalysis associated with microbial community shifts were investigated.WAS disintegration was boosted considerably by enzymolysis with 8750 mg/L of soluble COD release within 180 min.Mesophilic anaerobic fermentation(MAF)produced nearly equal VFA accumulation with over 3200 mg COD/L compared with that of thermophilic fermentation(TAF).Bacterial community consortia showed great shifting differences in dynamics of main T⁃RFs between MAF and TAF.Moreover,MAF was conducive to form intermediate bacterial community evenness compared to TAF,which preserved a robust function of VFA production.The enzymes catalysis prompted bio⁃energy(electricity)recovery potential of WAS organics via anaerobic fermentation(MAF/TAF)with evaluating electricity conversion efficiency of 0.75-0.82 kW·h/kg VSS(3.9 times higher than control test).Finally,this study proposed some novel thinking on future WAS treatment/management towards energy recovery coupled with energy⁃sufficient wastewater treatment by co⁃locating WAS anaerobic fermentation,MFC plant with wastewater treatment plant(s).

Effects of treatment time and temperature on the DC corona pretreatment performance of waste activated sludge

In order to improve the anaerobic digestion efficiency of waste activated sludge（WAS）,a pretreatment procedure should be carried out so as to disrupt the microbial cell structure,thus releasing intracellular organic matters.In this paper,a corona discharge triggered by a DC voltage was employed to pre-treat WAS for various time periods under different temperatures.The magnitude of the DC voltage was 4 k V at both negative and positive polarities.The changes in the soluble chemical oxygen demand,phosphorus and nitrogen content,and p H value within the WAS were utilized to estimate the pretreatment performance of the DC corona.It was found that with increasing treatment time,the pretreatment efficiency tends to be reduced.With increased temperature,the pretreatment efficiency appears to be better.It is suggested that the oxidative species and the active particles generated in the corona discharge play an important role in disrupting the microbial cell structure,which is dependent upon the treatment time and the temperature.

剩余污泥有机质资源回收利用原位驱动晚期垃圾渗滤液深度脱氮——一种具有显著能源优势的创新生物技术

The sustainable recovery and utilization of sludge bioenergy within a circular economy context has drawn increasing attention,but there is currently a shortage of reliable technology.This study presents an innovative biotechnology based on free nitrous acid(FNA)to realize sustainable organics recovery from waste activated sludge(WAS)in-situ,driving efficient nitrogen removal from ammonia rich mature landfill leachate by integrating partial nitrification,fermentation,and denitrification process(PN/DN-F/DN).First,ammonia((1708.5±142.9)mg·L^(-1))in mature landfill leachate is oxidized to nitrite in the aerobic stage of a partial nitrification coupling denitrification(PN/DN)sequencing batch reactor(SBR),with nitrite accumulation ratio of 95.4%±2.5%.Then,intermediate effluent(NO_(2)^(-)-N=(1196.9±184.2)mg·L^(-1))of the PN/DN-SBR,along with concentrated WAS(volatile solids(VSs)=(15119.8±2484.2)mg·L^(-1)),is fed into an anoxic reactor for fermentation coupling denitrification process(F/DN).FNA,the protonated form of nitrite,degrades organics in the WAS to the soluble fraction by the biocidal effect,and the released organics are utilized by denitrifiers to drive NOx-reduction.An ultra-fast sludge reduction rate of 4.89 kg·m^(-3)·d^(-1) and nitrogen removal rate of 0.46 kg·m^(-3)·d^(-1) were realized in the process.Finally,F/DN-SBR effluent containing organics is refluxed to PN/DN-SBR for secondary denitrification in the post anoxic stage.After 175 d operation,an average of 19350.6 mg chemical oxygen demand organics were recovered per operational cycle,with 95.2%nitrogen removal and 53.4%sludge reduction.PN/DN-F/DN is of great significance for promoting a paradigm transformation from energy consumption to energy neutral,specifically,the total benefit in equivalent terms of energy was 291.8 kW·h·t^(-1) total solid.

Combined alkaline and ultrasonic pretreatment of sludge before aerobic digestion

Alkaline and ultrasonic sludge disintegration can be used as the pretreatment of waste activated sludge （WAS） to promote the subsequent anaerobic or aerobic digestion. In this study, different combinations of these two methods were investigated. The evaluation was based on the quantity of soluble chemical oxygen demand （SCOD） in the pretreated sludge as well as the degradation of organic matter in the subsequent aerobic digestion. For WAS samples with combined pretreatment, the released COD levels were higher than those with ultrasonic or alkaline pretreatment alone. When combined with the ultrasonic treatment, NaOH treatment was more efficient than Ca（OH）2 for WAS solubilization. The COD levels released in various sequential options of combined NaOH and ultrasonic treatments were in the the following descending order： simultaneous treatment 〉 NaOH treatment followed by ultrasonic treatment 〉 ultrasonic treatment followed by NaOH treatment. For simultaneous treatment, low NaOH dosage （100 g/kg dry solid）, short duration （30 min） of NaOH treatment, and low ultrasonic specific energy （7500 kJ/kg dry solid） were suitable for sludge disintegration. Using combined NaOH and ultrasonic pretreatment with optimal parameters, the degradation efficiency of organic matter was increased from 38.0% to 50.7%, which is much higher than that with ultrasonic （42.5%） or with NaOH pretreatment （43.5%） in the subsequent aerobic digestion at the same retention time.

Recovery of Biomass Incinerated as Struvite-K Precipitates Followed Aluminium Removal

Phosphorus (P) and potassium (K) are non-renewable materials and widely in many industries such as agricultural sectors. On the other hand, the demand of P and K as fertilizers increases which following global population. The nutrient source of P and K which get from biomass waste i.e. incinerated of activated sludge and coffee husk biochar, respectively. The present study was conducted recovery of P and K as struvite-K (KMgPO4·6H2O) precipitates. The results showed that aluminium was released simultaneously with P from incinerated activated sludge with precipitate of Al:P of 1:1, K:P of 0.5, and Mg:P of 3. However, aluminium was inhibited to form struvite-K. Then, we examined cation removal especially for removed Al by dissolved 0.5 M HNO3 and the solution was mixed with KH2PO4 and MgCl2·6H2O as source of K and Mg, respectively. The results showed aluminium (Al) was removed with precipitate K:P of 0.5, and Mg:P of 0.8. This study was confirmed that recovery of biomass incinerated was successful as struvite-K and can be used as fertilizers.

Enhancement of thermophilic anaerobic digestion of thickened waste activated sludge by combined microwave and alkaline pretreatment

Pretreatment of thickened waste activated sludge （TWAS） by combined microwave and alkaline pretreatment （MAP） was studied to improve thermophilic anaerobic digestion efficiency. Uniform design was applied to determine the combination of target temperature （110-210°C）, microwave holding time （1-51 min）, and NaOH dose （0-2.5 g NaOH/g suspended solids （SS）） in terms of their effect on volatile suspended solids （VSS） solubilization. Maximum solubilization ratio （85.1%） of VSS was observed at 210°C with 0.2 g-NaOH/g-SS and 35 min holding time. The effects of 12 different pretreatment methods were investigated in 28 thermophilic batch reactors by monitoring cumulative methane production （CMP）. Improvements in methane production in the TWAS were directly related to the microwave and alkaline pretreatment of the sludge. The highest CMP was a 27% improvement over the control. In spite of the increase in soluble chemical oxygen demand concentration and the decrease in dewaterability of digested sludge, a semi-continuous thermophilic reactor fed with pretreated TWAS without neutralization （at 170~C with 1 min holding time and 0.05 g NaOH/g SS） was stable and functioned well, with volatile solid （VS） and total chemical oxygen demand （TCOD） reductions of 28% and 18%, respectively, which were higher than those of the control system. Additionally, methane yields （L@STP/g-CODaded, at standard temperature and pressure （STP） conditions of 0°C and 101.325 kPa） and （L@STP/g VSadad） increased by 17% and 13%, respectively, comoared to the control reactor.

Co-fermentation of waste activated sludge with food waste for short-chain fatty acids production:effect of pH at ambient temperature

Effect of pH ranging from 4.0 to 11.0 on cofermentation of waste activated sludge(WAS)with food waste for short-chain fatty acids(SCFAs)production at ambient temperature was investigated in this study.Experimental results showed that the addition of food waste significantly improved the performance of WAS fermentation system,which resulted in the increases of SCFAs production and substrate reduction.The SCFAs production at pH 6.0,7.0,8.0,and 9.0 and fermentation time of 4 d was respectively 5022.7,6540.5,8236.6,and 7911.7 mg COD·L^(-1),whereas in the blank tests(no pH adjustment,pH 8.0(blank test 1),no food waste addition,pH 8.0(blank test 2),and no WAS addition(blank test 3))it was only 1006.9,971.1,and 1468.5 mg COD·L^(-1),respectively.The composition of SCFAs at pH from 6.0 to 9.0 was also different from other conditions and propionic acid was the most prevalent SCFA,which was followed by acetic and n-butyric acids,while acetic acid was the top product under other conditions.At pH 8.0 a higher volatile suspended solids(VSS)reduction of 16.6%for the mixture of WAS and food waste than the sole WAS indicated a synergistic effect existing in fermentation system with WAS and food waste.The influence of pH on the variations of nutrient content was also studied during anaerobic fermentation of the mixture of WAS and food waste at different pH conditions.The release of NH_(4)^(+)-N increased with fermentation time at all pH values investigated except 4.0,5.0 and in blank test one.The concentrations of soluble phosphorus at acidic pHs and in the blank test one were higher than those obtained at alkaline pHs.Ammonia and phosphorus need to be removed before the SCFAsenriched fermentation liquid from WAS and food waste was used as the carbon source.

Effect of Ca:Mg ratio and high ammoniacal nitrogen on characteristics of struvite precipitated from waste activated sludge digester effluent

This study revealed the relationship between the presence of calcium impurities and ammoniacal nitrogen concentration upon crystallization of struvite.The research hypothesis was that the presence of both calcium and high concentrations of ammoniacal nitrogen(328–1000 mg/L)in waste activated sludge may influence the struvite quality and acid stability.Hence,we studied the impact of Ca:Mg ratio upon morphology,particle size,purity and dissolution of struvite,in the presence of varying levels of excess ammoniacal nitrogen.X-ray diffraction revealed that up to 31.4%amorphous material was made which was assigned to hydroxyapatite.Increasing the ammoniacal nitrogen concentration and elevation of the Mg:Ca ratio maximized the presence of struvite.Struvite particle size was also increased by ammoniacal nitrogen as was twinning of the crystals.Tests with dilute solutions of organic acid revealed the sensitivity of struvite dissolution to the physical characteristics of the struvite.Smaller particles(21.2μm)dissolved at higher rates than larger particles(35.86μm).However,struvite dissolved rapidly as the p H was further reduced irrespective of the physical characteristics.Therefore,addition of struvite to low p H soils was not viewed as beneficial in terms of controlled nutrient release.Overall,this study revealed that waste activated sludge effluent with high ammoniacal nitrogen was prospective for synthesis of high quality struvite material.

Effects of sludge age on anaerobic acidification of waste activated sludge: Volatile fatty acids production and phosphorus release

Effects of sludge age on volatile fatty acids (VFAs) production and Phosphorus (P) release during anaerobic acidification of waste activated sludge (WAS) were investigated.Sequencing batch reactors (SBR) fed with simulating domestic sewage were applied to produce WAS of different sludge ages,and batch tests were used for anaerobic acidification.The maximum dissolved total organic carbon,release of PO_(4)^(3+)-P,and accumulation of acetate (C2),propionate (C3),butyrate (C4),and valerate (C5) decreased by 56.2%,55.8%,52.6%,43.7%,82.4%and 84.8%,respectively,as the sludge age of WAS increased from 5 to 40 days.Limited degradation of protein played a dominating role in decreasing DTOC and VFAs production.Moreover,the increase in molecular weight of organics and organic nitrogen content in the supernatant after acidification suggested that the refractory protein in WAS increased as sludge age extended.Although the production of C2,C3,C4,and C5 from WAS decreased as the sludge age increased,the proportions of C2 and C3 in VFAs increased,which might be due to the declined production of C5 from protein and the faded genus Dechlorobacter.Keeping sludge age of WAS at a relatively low level (<10 days) is more appropriate for anaerobic acidification of WAS as internal carbon sources and P resource.

A new process to improve short-chain fatty acids and bio-methane generation from waste activated sludge

As an important intermediate product, short-chain fatty acids（SCFAs） can be generated after hydrolysis and acidification from waste activated sludge, and then can be transformed to methane during anaerobic digestion process. In order to obtain more SCFA and methane,most studies in literatures were centered on enhancing the hydrolysis of sludge anaerobic digestion which was proved as un-efficient. Though the alkaline pretreatment in our previous study increased both the hydrolysis and acidification processes, it had a vast chemical cost which was considered uneconomical. In this paper, a low energy consumption pretreatment method, i.e. enhanced the whole three stages of the anaerobic fermentation processes at the same time, was reported, by which hydrolysis and acidification were both enhanced, and the SCFA and methane generation can be significantly improved with a small quantity of chemical input. Firstly, the effect of different pretreated temperatures and pretreatment time on sludge hydrolyzation was compared. It was found that sludge pretreated at 100°C for 60 min can achieve the maximal hydrolyzation. Further, effects of different initial p Hs on acidification of the thermal pretreated sludge were investigated and the highest SCFA was observed at initial p H 9.0with fermentation time of 6 d, the production of which was 348.63 mg COD/g VSS（6.8 times higher than the blank test） and the acetic acid was dominant acid. Then, the mechanisms for this new pretreatment significantly improving SCFA production were discussed. Finally,the effect of this low energy consumption pretreatment on methane generation was investigated.

Compared effects of “solid-based” hydrogen peroxide pretreatment on disintegration and properties of waste activated sludge

The effects of two solid-based hydrogen peroxides sodium percarbonate(SPC) and calcium peroxide(CP)on waste activated sludge(WAS) disintegration were investigated. Both oxidants achieved efficient WAS disintegration for the synergistic effect of alkaline and oxidation. The strong alkaline condition led to the leakage of ammonia and the existence of abundant calcium ions accelerated the fixation of phosphorus via precipitation in CP WAS disintegration process. However, the spongy-like layer and low p H condition retarded the release of gaseous ammonia in SPC group. Hydroxyl radical was the main oxygen reactive species in SPC approaches which were more intense than CP by electron spin resonance(ESR) analysis.CP treated WAS contented more small particle size matter and total suspended solids(TSS) increased dramatically. In conclusion, CP pretreated sludge was more suitable for fertilization, while SPC was in favor of anaerobic digestion. This study clarified the differences between these two oxidants and their intermediates on nutrients release in sludge disintegration.

New insight into adsorption characteristics and mechanisms of the biosorbent from waste activated sludge for heavy metals

The adsorption characteristics and mechanisms of the biosorbent from waste activated sludge were investigated by adsorbing Pb2＋and Zn2＋in aqueous single-metal solutions. A p H value of the metal solutions at 6.0 was beneficial to the high adsorption quantity of the biosorbent. The optimal mass ratio of the biosorbent to metal ions was found to be 2. A higher adsorption quantity of the biosorbent was achieved by keeping the reaction temperature below 55°C. Response surface methodology was applied to optimize the biosorption processes, and the developed mathematical equations showed high determination coefficients（above 0.99 for both metal ions） and insignificant lack of fit（p = 0.0838 and 0.0782 for Pb2＋and Zn2＋, respectively）. Atomic force microscopy analyses suggested that the metal elements were adsorbed onto the biosorbent surface via electrostatic interaction. X-ray photoelectron spectroscopy analyses indicated the presence of complexation（between –NH2,-CN and metal ions） and ion-exchange（between –COOH and metal ions）. The adsorption mechanisms could be the combined action of electrostatic interaction, complexation and ion-exchange between functional groups and metal ions.