Co-pyrolysis of Sewage Sludge with Paint Sludge: Kinetics and Thermodynamic Analysis via Iso-conversional Methods

This study explored the synergistic interaction of sewage sludge(SS)and automotive paint sludge(PS)during co-pyrolysis for the optimized treatment of sewage sludge in cement kiln systems,utilizing thermogravimetric analysis(TGA)and thermogravimetric-mass spectrometry(TGA-MS).The result reveals the coexisting synergistic and antagonistic effects in the co-pyrolysis of SS/PS.The synergistic effect arises from hydrogen free radicals in SS and catalytic components in PS,while the main source of the antagonistic effect is that,during the mechanical mixing process,the SS/PS is converted from the particulate form into a dough-like rubbery which contributes to the film-forming effect,hindering the volatilization of volatile components.SS/PS co-pyrolysis reduces the yielding of tar production while increasing coke and gas.This study will provide some in-depth insights into the co-pyrolysis of SS/PS,and offer theoretical support for the subsequent research on the collaborative disposal processes in cement kilns.

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.

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.

Simultaneous removal of sulfur dioxide and nitrogen oxide from flue gas by phosphorus sludge:The performance and absorption mechanism

Developing low-cost and green simultaneous desulfurization and denitrification technologies is of great significance for sulfur dioxide(SO_(2))and nitrogen oxide(NO_(x))emission control at low temperatures,especially for small and medium-sized coal-fired boilers and furnaces.Herein,phosphorus sludge,an industrial waste from the production process of yellow phosphorus,has been developed to simultaneously eliminate SO_(2)and NO_(x)from coal-fired flue gas.The key factors affecting the experimental results indicate that desulfurization and denitrification efficiency of over 95%can be achieved at a low temperature of 55℃.Further,the absorption mechanism was investigated by characterizing the solid and liquid phases of the phosphorus sludge during the absorption process.The efficient removal of SO_(2)is attributed to the abundance of iron(Fe^(3+))and manganese(Mn^(2+))in the absorbent.SO_(2)can be rapidly catalyzed and converted to SO_(4)^(2-)by them.The key to NOx removal is the oxidation of NO toward watersoluble high-valent nitrogen oxides by oxidizing reactive substances induced via yellow phosphorus,which are then absorbed by water and converted to NO_(3)^(-).Meanwhile,yellow phosphorus is oxidized to phosphoric acid(H_(3)PO_(4)).The spent absorption slurry can be reused through wet process phosphoric acid production,as it contains sulfuric acid(H_(2)SO_(4)),nitric acid(HNO_(3)),and H_(3)PO_(4).Accordingly,this is a technology with broad application prospects.

Study on Mechanical Properties and Action Mechanism of Leather Industrial Sludge Aggregate Baking-Free Bricks

Taking an industrial sludge and its preparation of sludge wrap shell aggregates(WSAs)instead of sand to prepare baking-free brick as the research object,the development law of mechanical properties and the influence mechanism of macro and micro characteristic parameters of the bricks under different sludge and WSAs replacement rates were studied through the macroscopic mechanical properties test,with the help of nuclear magnetic resonance(NMR),transmission electron microscopy-energy spectrum and other testing technology and pores and cracks analysis system(PCAS)software.The results showed that the compressive strength of each sample decreased with the increase of sludge content.When the sludge content was less than 30%,it was mainly affected by the water-binder ratio.When the sludge content was more than 30%,it was mainly affected by the sludge content.At the age of 7 days,with the increase in replacement rate of WSAs,the compressive strength of the S10 and S30 groups was higher than that of the control group.The compressive strength of the S50 experimental group was 30.38 MPa,and the loss of compressive strength was slight compared with the control group.The water absorption rate of the 28 days S100 experimental group increased by 10.71%compared with the control group.When the content of WSAs was less than 50%,the holes above 0.1μm in the brick can be reduced and transformed into smaller holes,with a decreasing trend of the plane porosity of the brick.The microscopic results of the baking-free brick showed that the three-phase system of WSAs-interface transition area-mortar was poorly bonded and delaminated compared with the gravel aggregate-interface transition area-mortar system,and damage was more likely to occur in the WSAs and interface transition area.The above results show that it is feasible to use sludge and WSAs instead of sand for the preparation of baking-free bricks.This technology not only solves the problem of sludge disposal,but also protects the over-exploitation of mineral resources,and the technology has a broad application prospect and market value.

Nano-CaO_(2)Promotes the Release of Carbon Sources from Municipal Sludge and the Preparation of Double-Network Hydrogels with High Swelling Ratios

In this study,hydrogels were prepared from municipal sludge to recycle and realize the value-added utilization of the carbon components in this abundant waste material.The carbon sources were extracted from the municipal sludge using synthesised nano CaO_(2)as an oxidant,and the carbon sources were graft copolymerised with acrylic acid monomer using N,N′-methylenebisacrylamide as a crosslinking agent and ammonium persulfate as an initiator.The factors influencing the hydrogel preparation were investigated by single-factor experiments.Based on the results of the single-factor experiments,a hydrogel with a swelling ratio of up to 19768.4%at 12 h was prepared with an oxidant dosage of 0.20 g,a monomer dosage of 5.8 g,a neutralisation degree of the monomer of 70%,an initiator dosage of 0.15 g,and a crosslinking agent dosage of 0.15 g.The hydrogel preparation conditions were optimized using the response surface method,and the interactions between the different reaction conditions were analysed to obtain the best preparation conditions.X-ray diffraction results showed that hydrogels were amorphous in structure.Scanning electron microscopy images showed that the SiO_(2)particles from the sludge acted as crosslinking points between different layers of hydrogel chains.The crosslinking polymerisation and crosslinking agent worked together to form hydrogels with an inorganic-organic double network structure,and this structure was highly stretchable,resulting in hydrogels with good swelling properties.

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.

Treatment and Resource Utilization of Deinking Sludge from Regenerated Paper Mill

To fully utilize secondary resources,it will inevitably generate a large amount of deinking sludge using waste paper as raw material for paper making.The sludge contains small fibers and dissolved substances of various chemicals.After adding flocculant and settling treatment,deinked sludge is formed.However,its organic matter content can reach a high level of 40%to 50%,and it can also be reused,effectively avoiding the harmful impact of papermaking sludge on the environment.

Numerical Simulation of Vacuum Preloading for Chemically Conditioned Municipal Sludge

Municipal sludge is a sedimentation waste produced during the wastewater process in sewage treatment plants.Among recent studies,pilot and field tests showed that chemical conditioning combined with vacuum preloading can effectively treat municipal sludge.To further understand the drainage and consolidation characteristics of the conditioning sludge during vacuum preloading,a large deformation nonlinear numerical simulation model based on the equal strain condition was developed to simulate and analyze the pilot and field tests,whereas the simulation results were not satisfactory.The results of the numerical analysis of the pilot test showed that the predicted consolidation degree was greater than that measured by the field tests,which is attributed to the relatively low permeability layer formed during the preloading process of the prefabricated vertical drain.To better reflect the consolidation process of the conditioned sludge,a simplified analysis method considering the low permeability layer around the prefabricated vertical drain was proposed.The initial permeability coefficient of the low permeability layer is determined via numerical simulations using finite difference method.The predicted settlement curve was in good agreement with the measured results,which indicated that the numerical simulation based on the equal strain condition considering the relatively low permeability layer can better analyze the consolidation process of ferric chloride-conditioning sludge with vacuum preloading.

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.

Contribution to the Management of Fecal Sludge in the Urban Commune of Mamou(Republic of Guinea)

In the town of Mamou,all homes with sanitation systems are equipped with autonomous installations not connected to a sewer network.The emptying service is provided by manual emptiers and by the living environment and sanitation service of the urban municipality which has a single 6 m^(3)truck.The objective of this work is to determine the quantity of fecal sludge produced within the city for sustainable management.The methodology adopted is based on a field survey and the use of three methods for evaluating the quantities of sludge(specific production,quantity of sludge collected by the sludge truck and the total production of sludge produced in the various sludge works).The results obtained show that,out of the 2,940 sanitation works identified,2,936 works have been emptied at least once since their construction.Then 2,307 structures are emptied manually or 78.57%,against;619 structures emptied mechanically or 21.08%.The structures are emptied on average every 3 years for septic tanks and every 5 years for dry latrines.The specific production of sludge is 685,241,532 m^(3)/year;the production of sludge by the mechanical emptying technique varies from 588,641.57 m^(3)/year to 724,800.46 m^(3)/year and the production of sludge by manual emptying is 1,573,709.33 m^(3)/year,for a total quantity of sludge produced including between 2,162,350 m^(3)/year to 685,241,531.9 m^(3)/year.

PCR-DGGE法研究Sludge bio-membrane(SB)系统中反硝化聚磷菌的变化

采用SB同步脱氮除磷系统富集反硝化聚磷菌,利用平板分离法和PCR-DGGE技术,进行微生物种群的跟踪。研究结果表明:通过平板法分离到的微生物主要为棒状杆菌属、不动杆菌属、假单胞菌属、肠杆菌科、莫拉氏菌属、葡萄球菌属、副球菌属共7种,富集后细菌主要为不动杆菌属、假单胞菌属、肠杆菌科、副球菌属4种,富集后系统内细菌种类减少,与采用Sequencing Batch Reactor(SBR)池富集的反硝化聚磷菌不同。采用PCR-DGGE法发现富集前以黄杆菌属、产碱杆菌属、副球菌属、紫色杆菌属、赤细菌属为主,富集后以产碱杆菌属、副球菌属、紫色杆菌属为主,副球菌属是唯一通过2种办法获得确认的反硝化聚磷菌株。采用PCR-DGGE和16S rDNA克隆文库方法研究的同步反硝化聚磷菌都以变形门占优势。

Highsludge~工艺中氮的沿程变化与同步脱氮研究

采用Highsludge工艺处理城市污水,考察了氮的沿程变化与同步脱氮情况。结果表明,在第二好氧池中只发生了硝化作用,总氮无明显的下降;而在第一好氧池中总氮有明显的下降,去除率在16.8%～62.3%变化,平均去除率为33.19%,表明在该池中发生了明显的同步脱氮反应。该工艺的除污效果良好,对COD、BOD5、TN、NH4+-N的去除率分别为95%、96%、84%和82%,且污泥沉降性能良好,并未因污泥浓度高而发生丝状菌污泥膨胀、沉淀池污泥上浮等现象。

Analysis of bacterial community structures in two sewage treatment plants with different sludge properties and treatment performance by nested PCR-DGGE method

The bacterial community structures in two sewage treatment plants with different processes and performance were investigated by denaturing gradient gel electrophoresis （DGGE） of nested polymerase chain reaction （nested PCR） amplified 16S rRNA gene fragments with group-specific primers. Samples of raw sewage and treated effluents were amplified using the whole-cell PCR method, and the activated sludge samples were amplified using the extracted genomic DNA before the PCR products were loaded on the same DGGE gel for bacterial community analysis. Ammonia-oxidizing bacterial and actinomycetic community analysis were also carried out to investigate the relationship between specific population structures and system or sludge performance. The two plants demonstrated a similarity in bacterial community structures of raw sewage and activated sludge, but they had different effluent populations. Many dominant bacterial populations of raw sewage did not appear in the activated sludge samples, suggesting that the dominant bacterial populations in raw sewage might not play an important role during wastewater treatment. Although the two plants had different sludge properties in terms of settleability and foam forming ability, they demonstrated similar actinomycetic community structures. For activated sludge with bad settling performance, the treated water presented a similar DGGE pattern with that of activated sludge, indicating the nonselective washout of bacteria from the system. The plant with better ammonium removal efficiency showed higher ammonia-oxidizing bacteria species richness. Analysis of sequencing results showed that the major populations in raw sewage were uncultured bacterium, while in activated sludge the predominant populations were beta proteobacteria.

Performance of Anammox granular sludge bed reactor started up with nitrifying granular sludge

The anaerobic ammonia oxidation(Anammox) granular sludge bed reactor was started up successfully with nitrifying granular sludge. During the operation, the nitrifying granular sludge was gradually converted into Anammox granular sludge with good settling property and high conversion activity. The Anammox reactor worked well with the shortest HRT of 2 43 h. Under the condition that HRT w as 6 39 h and influent concentration of ammonia and nitrite was 10 mmol/L, the removal of ammonia and nitrite was 97 17% and 100 00%, respectively. Corresponding volumetric total nitrogen loading rate and volumetric total nitrogen conversion rate were 100 83 mmol/(L·d) and 98 95 mmol/(L·d). The performance of Anammox reactor was efficient and stable.

Effect of proteins,polysaccharides,and particle sizes on sludge dewaterability

Four batch experiments of hydrolysis and acidification were carried out to investigate the distributions of proteins （PN） and polysaccharides （PS） in the sludge, the PN/PS ratio, the particle sizes, and their relationship with sludge dewaterability （as determined by capillary suction time, CST）. The sludge flocs were stratified through centrifugation- and ultrasound-based method into four fractions： （1） slime, （2） loosely bound extracellular polymeric substances （LB-EPS）, （3） tightly bound EPS （TB-EPS）, and （4） pellet. The results showed that PN was mainly partitioned in the pellet （80.7%） and TB-EPS （9.6%） fractions, while PS distributed evenly in the four fractions. During hydrolysis and acidification, PN was transferred from the pellet and TB-EPS fractions to the slime fraction, but PS had no significant transfer trends. The mean particle sizes of the sludge flocs decreased with hydrolysis and acidification. The pH had a more significant influence on the dewaterability of sludge flocs than temperature. Sludge dewaterability during hydrolysis and acidification processes greatly deteriorated from 9.7 s at raw sludge to 340-450 s under alkaline conditions. However, it was just slightly increased under acidic conditions. Further investigation suggested that CST was affected by soluble PN, soluble PN/PS, and particle sizes of sludge flocs, but was affected slightly by total PN, PS, or PN/PS in the whole sludge flocs and other fractions （except slime）.

Effect of four crop straws on transformation of organic matter during sewage sludge composting

A 45-d laboratory experiment was conducted to compare the effect of four crop straws on the transformations of organic matter （OM） during composting of sewage sludge. The four crop straws included rape straw, wheat straw, maize straw and rice straw. The following parameters such as temperature, OM, humic-like substances （HS）, fulvic-like acids （FA） and humic-like acids （HA） were determined. The degradation of OM and the formation of HS and HA could be described well by the first-order kinetic model, while the FA content fluctuated during composting. The maximal degradation rates of OM in the compost piles added with rape straw, wheat straw, maize straw and rice straw were 34.7, 46.9, 54.7 and 52.8%, respectively, and the final contents of HS were 118, 128, 141 and 134 g kg-1, respectively, while the humification indices were higher in the compost piles added with maize straw and wheat straw than in those with rice straw and rape straw. The results indicate that a higher hemicellulose content and a lower C/N ratio in crop straw can result in a higher rate of OM degradation and higher contents of HS, while a higher content of lignin can lead to a higher polymerization degree of humic substances in compost piles. The final compost piles added with maize straw has the highest contents of OM, total nitrogen and humus substance as well as the highest values of polymerization degree, while compost piles with rape straw have the highest potassium content and those with rice straw have the highest pH values.

Optimization of process parameters for the bioconversion of activated sludge by Penicillium corylophilum, using response surface methodology

The optimization of process parameters for the bioconversion of activated sludge by Penicillium corylophilum was investigated using response surface methodology （RSM）. The three parameters namely temperature of 33℃, agitation of 150 r/min, and pH of 5 were chosen as center point from the previous study of fungal treatment. The experimental data on chemical oxygen demand （COD） removal （%） were fitted into a quadratic polynomial model using multiple regression analysis. The optimum process conditions were determined by analyzing response surface three-dimensional surface plot and contour plot and by solving the regression model equation with Design Expert software. Box-Behnken design technique under RSM was used to optimize their interactions, which showed that an incubation temperature of 32.5℃, agitation of 105 r/min, and pH of 5.5 were the best conditions. Under these conditions, the maximum predicted yield of COD removal was 98.43%. These optimum conditions were used to evaluate the trail experiment, and the maximum yield of COD removal was recorded as 98.5%.

Biosorption of cadmium(II) and lead(II) ions from aqueous solutions onto dried activated sludge

The removal of heavy-metal ions from aqueous solutions by using dried activated sludge has been investigated in batch systems. Effect of solution pH, initial metal ion concentration, and temperature were determined. The results of the kinetic studies showed that the uptake processes of the two metal ions（Cd（Ⅱ） and Pb（Ⅱ）） followed the pseudo-second-order rate expression. The equilibrium data fitted very well to both the Langmuir and Freundlich adsorption models. The FT-IR analysis showed that the main mechanism of Cd（Ⅱ） and Pb（Ⅱ） biosorption onto dried activated sludge was their binding with amide I group.

Plants grown on sewage sludge in South China and its relevance to sludge stabilization and metal removal

The production of sewage sludge in China has been increasing sharply in order to treat 40% of the municipal sewage in 2005 as planned by central government. The main sludge disposal method is landfill owing to heavy metal contamination, but it presents an attractive potential for agricultural land application. Experiments were carried out to study the simultaneous metal removal and sludge stabilization by plants. The sludge samples were collected from Datansha Wastewater Treatment Plant of Guangzhou, it contained excessive Cu and Zn compared with the Chinese National Standard for Agricultural Use of Sewage Sludge. Plants growing on sludge beds were investigated to follow their growth and metal uptake. 30 sludge plants were identified during 1 year's observation. A Zn high accumulating and high growth rate plant (Alocasia macrorrhiza) was selected and grown on sludge beds in plots. The water, organic matter, heavy metals and nutrients contents, the E. coli number and the cress seed germination index were monitored for the sludge samples collected monthly. The plant growth parameters and its heavy metals contents were also determined. The sewage sludge treated by plants could be stabilized at about 5 months, the E. coli number was significantly decreased and the cress seed germination index attained 100%. Crop on sludge could ameliorate the sludge drying. The experiments are continuing to find out the appropriate plant combination for simultaneous sludge stabilization and metal removal for an acceptable period. Comparisons between the proposed processes and other methods for treating produced sludge such as composting, chemical and bacterial leaching were discussed.