Effect of Combined Microwave-Ultrasonic Pretreatment on Anaerobic Biodegradability of Primary, Excess Activated and Mixed Sludge

This work deals with the effect of combined microwave-ultrasonic pretreatment on the anaerobic biodegradability of primary, excess activated and mixed sludge. The characteristics, biodegradability and anaerobic digester performance for untreated primary, excess activated and mixed sludge were compared to combined microwave-ultrasonic pretreated primary, excess activated and mixed sludge. All sludge samples were subjected to Microwave treatment at 2450 MHz, 800 W and 3 min followed by ultrasonic treatment at a density of 0.4 W/mL, amplitude of 90%, Intensity of 150 W, pulse of 55/5 for 6min. Methane production in pretreated primary sludge was significantly greater (11.9 ml/g TCOD) than the methane yield of the untreated primary sludge (7.9 ml/g TCOD). Cumulative methane production of pretreated Excess Activated Sludge (EAS) was higher (66.5 ml/g TCOD) than the methane yield from pretreated mixed sludge (44.1 ml/g TCOD). Furthermore, digested EAS showed significantly higher dewaterability (201 s) than digested primary sludge (305 s) or mixed sludge (522 s). The average Methane: Carbondioxide ratio from EAS (1.85) was higher than that for mixed untreated sludge (1.24). VS reduction was also higher for EAS than the other two sludge types. However, pretreatment of EAS resulted in significant reduction in dewaterability due to higher percentage of fine floc particles in the pretreated EAS.

Optimization of chemistry and process parameters for control of intermetallic formation in Mg sludges

Intermetallic formation in sludge during magnesium(Mg)melting,holding and high pressure die casting practices is a very important issue.But,very often it is overlooked by academia,original equipment manufacturers(OEM),metal ingot producers and even die casters.The aim of this study was to minimize the intermetallic formation in Mg sludge via the optimization of the chemistry and process parameters.The Al8Mn5 intermetallic particles were identified by the microstructure analysis based on the Al and Mn ratio.The design of experiment(DOE)technique,Taguchi method,was employed to minimize the intermetallic formation in the sludge of Mg alloys with various chemical compositions of Al,Mn,Fe,and different process parameters,holding temperature and holding time.The sludge yield(SY)and intermetallic size(IS)was selected as two responses.The optimum combination of the levels in terms of minimizing the intermetallic formation were 9 wt.%Al,0.15 wt.%Mn,0.001 wt.%(10 ppm)Fe,690℃ for the holding temperature and holding at 30 mins for the holding time,respectively.The best combination for smallest intermetallic size were 9 wt.%Al,0.15 wt.%Mn,0.001 wt.%(10 ppm)Fe,630℃ for the holding temperature and holding at 60 mins for the holding time,respectively.Three groups of sludge factors,Chemical Sludge(CSF),Physical Sludge(PSF)and Comprehensive Sludge Factors(and CPSF)were established for prediction of sludge yields and intermetallic sizes in Al-containing Mg alloys.The CPSF with five independent variables including both chemical elements and process parameters gave high accuracy in prediction,as the prediction of the PSF with only the two processing parameters of the melt holding temperature and time showed a relatively large deviation from the experimental data.The Chemical Sludge Factor was primarily designed for small ingot producers and die casters with a limited melting and holding capacity,of which process parameters could be fixed easily.The Physical Sludge Factor could be used for mass production with a single type of Mg alloy,in which the chemistry fluctuation might be negligible.In large Mg casting suppliers with multiple melting and holding furnaces and a number of Mg alloys in production,the Comprehensive Sludge Factor should be implemented to diminish the sludge formation.

Releasing characteristics of phosphorus and other substances during thermal treatment of excess sludge

The releasing characteristics of phosphorus, nitrogen compounds, organics, and some metal cations during thermal treatment of excess sludge were investigated. It was found that during heating not only phosphorus, but also nitrogen compounds, organics, and some metal cations could be released in abundance. The maximum orthophosphate （ortho-P） release of about 90 mg/L in concentration was observed at 50℃ in 1 h. Except for volatile fatty acids （VFAs）, comparatively little total nitrogen （TN）, total organic carbon （TOC）, and metal cations were released at the same time. Such results might favor further process of phosphorus recovery. VFAs were considerably released only at 50℃. Acetic, butyric, and propionic acid were the most abundant components in turn and their releasing profiles exhibited good linear relationship with time （R2 = 0.9977, 0.9624, and 0.8908, respectively）. The concentrations of Mg^2＋ and K^＋ increased with time and temperature during thermal treatment, but Ca^2＋ decreased. The release of Mg^2＋ and K^＋ agreed well with TP release （R^2 = 0.9892 and 0.9476, respectively）. Temperature in the experimental range had very little impact on the linear relationships, especially of Mg^2＋. Moreover, the parameter of mixed liquor suspended solids （MLSS） was found to be an important factor for thermal sludge treatment as the released ortho-P and total phosphorus （TP） at 50℃ increased more than one-fold when MLSS was increased from 4000 to 8000 mg/L.

Removal of heavy metals from sewage sludge by low costing chemical method and recycling in agriculture

Experiments were carried out to study the removal of heavy metals from municipal sewage sludge by proper method for land application. The sequential extractions for metal fractionation showed that the non digested sludge from Guangzhou contained Cu and Zn principally bound to carbonate and oxides and the metal sulfides were low. Among H 2SO 4, EDTA and NH 4HCO 3 extractant agents, H 2SO 4 was the most efficient and economic in removing the heavy metals, especially with the addition of the concentrated acid. Plant experiment in pots with Chinese cabbage ( Brassica Chinensis ) showed that the acidified sludges neutralized with alkaline amendments such as phosphate rock could increase significantly the plant yield and decreased the soil and plant contamination by heavy metals originated from sewage sludge.

A novel approach to treat combined domestic wastewater and excess sludge in MBR

Domestic wastewater was treated by combined anaerobic biofilm aerobic membrane bioreactor(MBR) process, and part biomass in MBR was withdrawn to treat with ozone, then the ozonated sludge was returned to anaerobic inlet. In aerobic MBR, MLSS and DO were controlled at 3000—3500 mg/L and 0 8 mg/L respectively. Comparing the experimental results of two stages, it was noticed that ozonation did not affect the removal efficiency for organics but had a significant influence on the removals of NH 3 N and TN. During the ozonation period of two months, no excess sludge was wasted, and a zero sludge yield was obtained.

Exploring the Performance of Magnetic Immobilized Lysozyme on Sludge Hydrolysis and Mechanism of Improving Dewaterability of Excess Sludge

The performance of the immobilized lysozyme and the native lysozyme on enhancing the excess sludge dewaterability was investigated.The results indicated that the specific resistance to filtration(SRF)decreased by 62.8%for native lysozyme and 53.6%for immobilized lysozyme at the enzyme dosage of 9 mg/g(dry sludge).Correlation analysis was carried out to explore the role of different extracellular polymeric substance(EPS)fractions on excess sludge dewaterability.The results illustrated that the SRF negatively correlated with protein,polysaccharide from soluble EPS(S-EPS)and loosely bound EPS(LB-EPS)and positively correlated with that from tightly bound EPS(TB-EPS).Three-dimensional excitation emission matrix(3D-EEM)fluorescence analysis combined with the scanning electron microscope(SEM)images,revealed that sludge floc structure and microbial cells were destroyed by enzymatic treatment,and that the enzymatic hydrolysis could help to improve the transformation of hydrophilic groups from TB-EPS and the performance of the excess sludge dewatering process.The assessment of hydrolysis using the immobilized enzyme provided a new insight for the safe disposal of the sludge.

Main Pathways in Primary Sludge Disintegration by Sonication and Enhancement of Sonication

The main pathways of primary sludge(PS)ultrasonic disintegration were analyzed at the sonication frequency of 20 kH z and the thermal effect on PS disintegration was investigated.By adding Na HCO3as a scavenger to entrap the free hydroxyl radicals,cavitation contributed to 82.91%of the total sonication effect.The power consumed by temperature rising accounted for more than40%of ultrasound power input at the power density of 0.215 W/m L and the sonication time of 10 min.With the thermal insulation of polyfoam coating during sonication,a 18.37%of soluble chemical oxygen demand(SCOD)increment was observed.With the process of pre-heating the PS before sonication,64.15%of SCOD increment was achieved.Compared with the particle size of 13.77μm for the sonicated PS,the sludge mean particle size decreased to 12.83 and11.98μm by applying polyfoam coating and pre-heating the PS to enhance the cavitation and thermal effect.It suggested that if thermal energy consumption was relieved during the sonication process of PS,more energy could be used to disintegrate the sludge.

Concentration and Chemical Speciation of Heavy Metals in Sludge and Removal of Metals by Bio-surfactants Application

The concentration and chemical speciation of heavy metals including REEs （rare earth elements）, Th （thorium） and U （uranium） in domestic sludge and electroplating sludge were investigated, and those of the domestic sludge were compared with those of natural soil. Removal of heavy metals in electroplating sludge was studied with bio-surfactants （saponin and sophorolipid） by batch and column experiments. The results suggested that heavy metals have greater concentrations and exist as more relatively unstable fraction in sludge than those in Natural soil. Nonionic saponin is more efficient than sophorolipid for the removal of heavy metals from the electroplating sludge, and mainly reacts with carbonate state （i.e., F3） and Fe-Mn oxide state （i.e., F5） fractions. The recovery efficiency of heavy metals in leachates from the electroplate sludge was attained 88%-97%. Saponin can be reused and be a promising and cost-effective material for the removal of heavy metals in sludge.

Treating both wastewater and excess sludge with an innovative process

The innovative process consists of biological unit for wastewater treatment and ozonation unit for excess sludge treatment. An aerobic membrane bioreactor(MBR) was used to remove organics and nitrogen, and an anaerobic reactor was added to the biological unit for the release of phosphorus contained at aerobic sludge to enhance the removal of phosphorus. For the excess sludge produced in the MBR, which was fed to ozone contact column and reacted with ozone, then the ozonated sludge was returned to the MBR for further biological treatment. Experimental results showed that this process could remove organics, nitrogen and phosphorus efficiently, and the removals for COD, NH 3-N, TN and TP were 93.17%, 97.57%, 82.77% and 79.5%, respectively. Batch test indicated that the specific nitrification rate and specific denitrification rate of the MBR were 1.03 mg NH 3-N/(gMLSS·h) and 0.56 mg NOx-N/(gMLSS·h), and denitrification seems to be the rate-limiting step. Under the test conditions, the sludge concentration in the MBR was kept at 5000—6000 mg/L, and the wasted sludge was ozonated at an ozone dosage of 0.10 kgO 3/kgSS. During the experimental period of two months, no excess sludge was wasted, and a zero withdrawal of excess sludge was implemented. Through economic analysis, it was found that an additional ozonation operating cost for treatment of both wastewater and excess sludge was only 0.045 RMB Yuan(USD 0.0054)/m 3 wastewater.

Preliminary Study on the Treatment Efficiency of Pasteurized Lime Thermal Alkaline Hydrolysis for Excess Activated Sludge and Reduction of Tetracycline Resistance Genes

Thermal alkaline hydrolysis is a common pretreatment method for the utilization of excess activated sludge(EAS).Owing to strict environment laws and need for better energy utilization,new methods were developed in this study to improve the efficiency of pretreatment method.Direct thermal hydrolysis(TH),pasteurized thermal hydrolysis(PTH),and alkaline pasteurized thermal hydrolysis(PTH+CaO and PTH+NaOH)methods were used to treat EAS.Each method was compared and analyzed in terms of dissolution in ammonium nitrogen(NH_(4)^(+)-N)and soluble COD(SCOD)in EAS.Furthermore,the removal of tetracycline resistance genes(TRGs)and class 1 transposon gene intI1 from EAS was investigated.The NH_(4)^(+)-N and SCOD concentrations in EAS treated by PTH were 1.24 and 2.58 times higher than those of TH.However,the removal efficiency of total TRGs and intI1 between the groups was comparable.The SCOD concentration of the PTH+NaOH group was 4.37 times higher than that of the PTH group,and the removal efficiency of total TRGs was increased by 9.52%compared with that by PTH.The NH_(4)^(+)-N and SCOD concentrations of the PTH+CaO group could reach 85.04%and 92.14%of the PTH+NaOH group,but the removal efficiency of total TRGs by PTH+CaO was 19.78%lower than that by PTH+NaOH.Thus,to reduce the financial cost in actual operation,lime(CaO)can be used instead of a strong alkali(NaOH),and pasteurized steam at 70℃ instead of conventional high-temperature heating to treat EAS.This study provides a reference for the development of alkaline hydrolysis under moderate temperatures along with the removal of TRGs in EAS.

Probiotic levels, chemical composition and fermentative characteristics in solid state fermentation of paper sludge for animal feeding

The sludge paper of the industry treated with probiotics in solid state fermentation (SSF) could be used as ingredient in rations for animal feeding. This study assessed the effect of four probiotic (Prozoot15?) levels (PT) on chemical and fermentative characteristics in SSF of the paper sludge (PS) at controlled temperature (30°C) in laboratory scale. The tested treatments (T) were: T1 (0% PS), T2 (50 g/kg PS), T3 (100 g/kg PS) and T4 (150 g/kg PS), which were fermented at 0, 24, 48 and 72 h, according to a completely randomized design, in a 4 × 4 factorial arrangement with six repetitions per sampling. All treatments included (g/kg DM) 300 molasses, 15 urea, 20 ammonium sulfate, 9 calcium carbonate and 5 of vitamin and mineral premix, plus the PS which was substituted by the PT at 0, 50, 100 and 150 g/kg DM. The results showed a decrease in pH in all treatments at 24 h;however the lowest pH was at 72 h of fermentation. At 72 h of fermentation, the PT addition in T4 increased crude protein, true protein and yeast counts

Comparative short-term effects of sewage sludge and its biochar on soil properties, maize growth and uptake of nutrients on a tropical clay soil in Zimbabwe

Soil application of biochar from sewage could potentially enhance carbon sequestration and close urban nutrient balances. In sub-Saharan Africa, comparative studies investigating plant growth effect and nutrients uptake on tropical soils amended with sewage sludge and its biochar are very limited. A pot experiment was conducted to investigate the effects of sewage sludge and its biochar on soil chemical properties, maize nutrient and heavy metal uptake, growth and biomass partitioning on a tropical clayey soil. The study compared three organic amendments; sewage sludge （SS）, sludge biochar （SB） and their combination （SS＋SB） to the unamended control and inorganic fertilizers. Organic amendments were applied at a rate of 15 t ha-1 for SS and SB, and 7.5 t ha-1 each for SS and SB. Maize growth, biomass production and nutrient uptake were significantly improved in biochar and sewage sludge amendments compared to the unamended control. Comparable results were observed with F, SS and SS＋SB on maize growth at 49 d of sowing. Maize growth for SB, SS, SS＋SB and F increased by 42, 53, 47, and 49%, respectively compared to the unamended control. Total biomass for SB, SS, SS＋SB, and F increased by 270,428, 329, and 429%, respectively compared with the unamended control. Biochar amendments reduced Pb, Cu and Zn uptakes by about 22% compared with sludge alone treatment in maize plants. However, there is need for future research based on the current pot experiment to determine whether the same results can be produced under field conditions.

Heavy Metals and PAHs in Sewage Sludge from Twelve Wastewater Treatment Plants in Zhejiang Province

Objective To investigate the heavy metals （HMs） and polycyclic aromatic hydrocarbons （PAHs） in sludge of twelve wastewater treatment plants （WWTPs） in Zhejiang province of China, and to assess their potential for land application. Methods Sludge was collected from 12 WWTPs within the province. GC-MS and AAS were used to measure PAHs and HMs contents in sludge. Results Concentrations of HMs in most of the sludge samples were below the regulatory limits for the sludge to be used in agriculture in China with the exception of Zn in 2 sludge samples and Cd in 1 sample. All 16 PAHs, targeted by the USEPA agency, were found in the sludge from the twelve plants with a total concentration ranging from 33.73 mg kg^-1 to 82.58 mg kg^-1 （dry weight, d.w.）. The levels of Σ9 PAHs varied from 13.87 mg kg^-1 to 61.86 mg kg^-1 （d.w.） in the sludge, far exceeding the limitation value recommended by the Europe Union. The concentration and composition of PAHs in sewage sludge varied and depended mainly on the quantity and type of industrial wastewater accepted by the WWTPs. A significant relationship between the proportion of industrial wastewater received by WWTPs and the total content of 16 PAHs in the sludge was observed. Conclusion PAHs have become one of the primary pollutants in sludge of Zhejiang WWTPs instead of HMs. It is, therefore, essential to reduce the contents of PAHs before the sludge can be used in agriculture through proper treatment.

Enhancing excess sludge aerobic digestion with low intensity ultrasound

In order to enhance the efficiency of aerobic digestion, the excess sludge was irradiated by low intensity ultrasound at a frequency of 28 kHz and acoustic intensity of 0.53 W/cm^2. The results show that the sludge stabilization without ultrasonic treatment can be achieved after 17 d of digestion, whereas the digestion time of ultrasonic groups can be cut by 3-7 d. During the same digestion elapsing, in ultrasonic groups the total volatile suspended solid removal rate is higher than that in the control group. The kinetics of aerobic digestion of excess sludge with ultrasound can also be described with first-order reaction.

Hydrolysis and acidification of activated sludge from a petroleum refinery

The cost-effective treatment of activated sludge that is generated by refining petroleum is a challenging industrial problem.In this study, semi-continuous stirred tank reactors(CSTRs) containing petroleum refinery excess activated sludge(PREAS)were used to comparatively investigate hydrolysis and acidification rates, after the addition of heneicosane(C_(21)H_(44))(R1)and 1-phenylnaphthalene(C16 H12)(R2) to different and individual reactors. Operation of the reactors using a sludge retention time(SRT) of 6 days and a pH of 5.0, resulted in the maintenance of stable biological activity as determined by soluble chemical oxygen demand(SCOD), volatile fatty acids(VFAs) production and oil removal efficiency. The optimum conditions for hydrogen production include a SRT of 8 days, at pH 6.5. Under these conditions, hydrogen production rates in the control containing only PREAS were 1567 mL/L(R0), compared with 1365 mL/L in Rl and 1454 mL/L-PREAS in R2.Coprothermobacter, Fervidobacterium, Caldisericum and Tepidiphilus were the dominant bacterial genera that have the potential to degrade petroleum compounds and generate VFAs. This study has shown that high concentrations of heneicosane and 1-phenylnaphthalene did not inhibit the hydrolytic acidification of PREAS.

Influence of Synthesis Temperature on Phosphate Adsorption by Zn-Al Layered Double Hydroxides in Excess Sludge Liquor

A group of Zn-Al layered double hydroxides (LDHs) were synthesized at different temperatures from 25-90 °C in order to investigate the influence of synthesis temperature on characteristics of the LDHs and their phosphate adsorption behaviour. The results reveal that an increase in the synthesis temperature generally improves the specific surface area of the sample and the phosphate adsorption capacity. The significantly enhanced crystallin- ity of the Zn-Al-30, synthesized at 30 °C, leads to a remarkable decrease in the specific surface area and consequently a poor phosphate adsorption capacity. It is suggested that the surface adsorption plays an important role in the phosphate uptake by the Zn-Al LDHs. Zn-Al-70 presents a relatively higher crystallinity and a lower specific surface area, compared with Zn-Al-60 and Zn-Al-80, but the highest phosphate adsorption capacity, indicating that surface adsorption is only one of the pathways for phosphate removal. The phosphate adsorption by the Zn-Al follows a pseudo-second-order kinetic equation. The adsorption isotherms fit Langmuir models, and the maximum a dsorption capacities of the Zn-Al-25, Zn-Al-50 and Zn-Al-70 are estimated to be 17.82, 21.01 and 27.10 mg·g-1 adsorbent, respectively.

Chemical looping gasification of sewage sludge using copper slag modified by NiO as an oxygen carrier

Chemical looping gasification(CLG) provides a novel approach to dispose the sewage sludge.In order to improve the reactivity of the calcined copper slag,NiO modification is considered as one of the good solutions.The copper slag calcined at 1100℃ doped with 20 wt% NiO(Ni20-CS) was used as an oxygen carrier(OC) in sludge CLG in the work.The modification of NiO can evidently enhance the reactivity of copper slag to promote the sludge conversion,especially for sludge char conversion.The carbon conversion and valid gas yield(V_(g)) increase from 67.02% and 0.23 m^(3)·kg^(-1) using the original OC to 78.34% and 0.29 m^(3)·kg^(-1) using the Ni20-CS OC, respectively.The increase of equivalent coefficient(Ω) facilitates the sludge conversion and a suitable Ω value is determined at 0.47 to obtain the highest valid gas yield(0.29 m^(3)·kg^(-1)).A suitable steam content is assigned at 27.22% to obtain the maximum carbon conversion of 87.09%,where an acceptable LHV of 12.63 MJ·m^(-3) and Vg of 0.39 m^(3)·kg^(-1)are obtained.Although the reactivity of Ni20-CS OC gradually decreases with the increase in cycle numbers because of the generation of NiFe_(2) O_(4-δ) species,the deposition of sludge ash containing many metallic elements is beneficial to the sludge conversion.As a result,the carbon conversion shows a slight uptrend with the increase of cycle numbers in sludge CLG.It indicates that the Ni20-CS sample is a good OC for sludge CLG.

The Effect on Activated Sludge of Chemical Coagulants Applied in Synchronization Dephosphorization

Combined with the practical experience of wastewater treatment plant, the chemical coagulants have inhibition effects on microorganism activity, with the influence degree of PAC (polyaluminium chloride) > AlCl3> Fe2(SO4)3. In synchronization dephosphorization, the inhibition rates of PAC in 10 ppm and 20 ppm are 11.9% and 33% respectively;while the inhibition rates of AlCl3 and Fe2(SO4)3 in 20 ppm are 15.8% and 8.5% respectively, compared with 9.6% and 5.4% in 10 ppm. Backwash wastewater from sand filter after adding coagulants has no direct inhibition effect on microorganism, but it results in inorganic components increase in active sludge. By taking North STP as an example, the VSS/SS ratio reduced from 0.65 after coagulants application to 0.54.

Kinetics of aerobically activated sludge on terylene artificial silk printing and dyeing wastewater treatment

Aerobically activated sludge processing was carried out to treat terylene artificial silk printing and dyeing wastewater (TPD wastewater) in a lab-scale experiment, focusing on the kinetics of the COD removal. The kinetics pa-rameters determined from experiment were applied to evaluate the biological treatability of wastewater. Experiments showed that COD removal could be divided into two stages, in which the ratio BOD/COD (B/C) was the key factor for stage division. At the rapid-removal stage with B/C>0.1, COD removal could be described by a zero order reaction. At the mod-erate-removal stage with B/C<0.1, COD removal could be described by a first order reaction. Then Monod equation was introduced to indicate COD removal. The reaction rate constant (K) and half saturation constant (KS) were 0.0208-0.0642 L/(gMLSS)h and 0.44-0.59 (gCOD)/L respectively at 20 C-35 C. Activation energy (Ea) was 6.05104 J/mol. By comparison of kinetic parameters, the biological treatability of TPD wastewater was superior to that of traditional textile wastewater. But COD removal from TPD-wastewater was much more difficult than that from domestic and industrial wastewater, such as papermaking, beer, phenol wastewater, etc. The expected effluent quality strongly related to un-biodegradable COD and kinetics rather than total COD. The results provide useful basis for further scaling up and efficient operation of TPD wastewater treatment.

Sludge ozonation and its effect on performance of submerged membrane bio-reactor

To investigate the effects of ozonation on minimizing the excess sludge and enhancing the nitrogen removal in an effluent, batch and continuous experiments in two MBRs with and without sludge ozonation （ namely combined and reference run） were carried out. Through ozonation at a dose of 0. 16 mg O3/mg MLVSS, 53.1% of the treated MLVSS was solubilized, and soluble SCOD/TN ratio of ozonized sludge （OS） was about 8. 6 due to the release of cellular nitrogen-contained materials and SCOD loss by ozone mineralization. In addition, the results of batch nitrification and denitrification tests with OS supernatant indicated that solubilized sludge could act as a reducing power for denitrification and a nitrogen source for nitrification. 40-day operation of-two MBR systems demonstrated that the recirculation of OS into a bioreaetor enabled the combined system have two advantages over the control one. The observed sludge yield （Yobs） was decreased from 0. 13 to 0. 06g MLSS/g COD, while the nitrogen removal was increased from 64. 6% to 72. 3%. And sludge ozonation elevated the inorganic fraction of MLSS, but did not impact sludge activities.