pH Value Of Sludge Research Articles

Characterization of heavy metals in textile sludge with hydrothermal carbonization treatment

Presence of heavy metals in sludge can severely limit land application due to their bioavailability. The current work studied distribution and risk as well as leaching toxicity of heavy metals in textile sludge treated with hydrothermal carbonization (HTC) at different conditions. Treatment temperature and time can significantly affect characteristics of heavy metals in sludge. For the treatment at 220 °C and 3 h, the content of Cu, Cr, Mn, and Zn existed in form F1 + F2 (water soluble and bound to carbonate and Fe-Mn oxides) dropped by 4.7, 7.1, 8.8, and 7.3%, while the content of Cu, Cr, and Mn in form F4 (bound to quartz, feldspars, etc) increased by 12.9, 19.1, and 10.6%, respectively. This effectively lowered the bioavailability and leaching rate of heavy metals in sludge. Addition of weak alkaline Al(OH)3 could efficiently force the transformation of F1 to F4, possibly because of the increased pH value of sludge. HTC processing might be an effective way of fixing heavy metals in textile sludge.

Analysis of the relationship of extracellular polymeric substances to the dewaterability and rheological properties of sludge treated by acidification and anaerobic mesophilic digestion

The initial pH value of sludge affects sludge anaerobic digestion and dewatering performance. In order to determine the suitable pH value and decrease the sludge digestion time, in this study, the effect and the mechanism of combined acidification and anaerobic mesophilic digestion (acid-AMD) on sludge dewaterability were investigated. The changes and relationships among the extracellular polymeric substances (EPS), physicochemical properties, and rheological behavior of the treated sludge were analyzed. The results indicated that the combined acid-AMD treatment improved sludge dewaterability approximately 36.08% and 30.28% compared to the acid conditioning and AMD treatment, respectively. The factors improving sludge dewaterability include a lower sludge pH value and appropriate duration of AMD, changes in particle size, surface properties and distribution of the EPS fractions. The acid-AMD treatment hydrolyzed the EPS, loosening the sludge structure. These changes reflected in the rheological properties of the sludge. After the treatment, the network strength and colloid force of the sludge weakened. The linear viscoelastic region contracted, and the sludge system became sensitive to shear. These results demonstrated that rheological analysis can help explain the sludge dewatering mechanism. The acid-AMD treatment effectively changed the distribution of EPS that play a vital role in sludge dewaterability.

Heavy metals in sludge during anaerobic sanitary landfill: Speciation transformation and phytotoxicity

Sanitary landfill persists as a predominant sludge disposal method in particular in China. In this study, successive subsurface sludge samples (0.3 m deep) were collected from a bioreactor landfill unit where an anaerobic process took place during a 500 d period. The sludge samples were analyzed for total concentrations of cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb) and zinc (Zn) and their species distributions, together with selected sludge chemical properties. In addition, the sludge samples were subjected to phytotoxicity testing. The results showed that the mobilities of Cd and Ni were decreased with landfill time, while the mobilities of Cr, Cu, Pb and Zn remained consistently low over the landfill period. The residual amounts of all these heavy metals were increased with landfill time, suggesting that the anaerobic sanitary landfill is an effective sludge stabilization method to reduce the ecological risk of these heavy metals. The increase in the sludge pH value with landfill time tended to promote the precipitation of heavy metals. Moreover, the sludge stabilization was found to be indicated by the formation of humic substance (HS) and volatilization of volatile matter (VM). The germination index (GI) values of barley (Hordeum vulgare L.) and Chinese cabbage (Brassica rapa chinensis) seeds grown in the 500 d anaerobically stabilized sludge were approximately 5.2- and 4.1-times higher than the values of those grown in the fresh sludge. The final sludge extract did not cause any significant inhibitory effect on the germination of the two types of seeds.

Effect of deflocculation on the efficiency of sludge reduction by Fenton process.

A novel approach to improve the efficiency of Fenton treatment for sludge reduction through the implication of a deflocculating agent citric acid, for the exclusion of extracellular polymeric substances (EPS) from waste-activated sludge (WAS), was investigated. Deflocculation was achieved with 0.06g/g suspended solids (SS) of citric acid dosage. Fenton optimization studies using response surface methodology (RSM) revealed that 0.5 and 0.0055g/g SS were the optimal dosages of H2O2 and Fe(2+). The addition of a cation-binding agent set the pH value of sludge to 5 which did not affect the Fenton efficiency. The results presented in this study shows the advantage of deflocculating the sludge as SS and volatile suspended solids (VSS) reductions were found to be higher in the deflocculated (53 and 63%, respectively) than in the flocculated (22 and 34%, respectively) sludges. Kinetic investigation of the treatment showed that the rate of the reaction was four times higher in the deflocculated sludge than control. The methodology reported in this manuscript was successfully applied to a real case were the deflocculated mediated Fenton process reduced the sludge disposal cost from 297.8 to 61.9 US dollars/ton of sludge.

Status evaluation of heavy metals in waste disposal sites of champion breweries and plasto crown company, Uyo, Akwa Ibom State, Nigeria

Sludge and soil samples were collected through purposive sampling method within Champion Breweries and Plasto Crown Company waste disposal sites during wet and dry seasons for status evaluation of their heavy metals (Fe, Pb, Zn, Ni, Cr, Cd, Co and Hg) for comparison with the control site and the world threshold standards for tropical soils. The results showed that the sludge pH value of 7.89 during wet season signified alkaline medium (outside the natural range of acidic medium for soils in the Niger Delta region of Nigeria) which was attributed to the high calcium content of the brewery effluent. The 7.42 pH value during wet season for soil in the Plasto Crown Company waste disposal site indicated alkaline medium which was due to the remnants of the wastes which formed lime to neutralize the acidic medium of the soil while the electrical conductivity values (below 4 dSm-1) indicated the nonsalinity of the soils. More so, a two way analysis of variance (ANOVA) statistical method used to run the analysis revealed that the soil in terms of heavy metal concentrations did not exceed the world threshold standards.Keywords: Soil, sludge, heavy metal concentrations, permissible standards.

Electrochemical Disintegration of Activated Sludge Using Ti/RuO<sub>2</sub> Anode

Electrochemical process is one of the most effective methods to enhance sludge disintegration. In this study, Ti/RuO2 anodes were prepared by Pechini’s method and the electrode surface morphology was characterized by FESEM and EDAX. The effects of various operating conditions were investigated including initial pH value of sludge, sludge concentration, electrolysis time and current density. The study showed that the removal efficiencies of TS, VS, TSS and VSS increased with the increase of pH in the alkaline range, electrolysis time and current density but decreased with the increase of initial sludge concentration. The application of electrochemical process using Ti/RuO2 electrodes enhanced the sludge disintegration for possible subsequent biological treatment.

Extracellular polymeric substances and bound water drastically affect bioleached sludge dewaterability at low temperature

It is well documented that bioleaching with the co-inoculation of Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans can drastically enhance sludge dewaterability under ambient temperature condition, but little information on low temperature effect on bioleached sludge dewaterability is available. In this study, the optimum sludge retention time of bioleaching treatment and the mechanisms responsible for the dewaterability enhancement of bioleached sludge were studied in two bioleaching systems conducted at a low temperature of 10°C and a normal temperature of 28°C, respectively. Results showed that Acidithiobacillus bacteria involved in the bioleaching were still active at 10°C, and sludge capillary suction time (CST) decreased in the first 3 days of bioleaching. Nevertheless, the degree of sludge dewaterability enhancement by bioleaching was much lower at 10°C than that at 28°C. The only slight decreases in the sludge pH value and relative high contents of extracellular polymeric substances (EPS) and bound water at a low temperature were responsible for the relatively lower dewaterability enhancement of bioleached sludge compared to that at the normal temperature. Moreover, statistical results showed that sludge CST had significant positive correlations with the sludge pH value, and EPS and bound water contents in the optimum bioleaching process (from day 0 to day 3). Therefore, reducing medium pH, and/or removing EPS from bioleaching bacteria and bound water of bioleached sludge through forced physical–chemical approaches prior to mechanical dewatering might be a good method to greatly improve sludge dewatering at a low temperature.

Dewatering of bio-sludge from industrial wastewater plant using an electrokinetic-assisted process: Effects of electrical gradient

An electrokinetic-assisted sludge dewatering (EASD) process was used to evaluate the dewaterability of the bio-sludge cake with moisture content of 68.9%. The cake sample was collected immediately after a belt filter press of an industrial wastewater treatment plant. Results showed that an average of electro-osmosis permeability of 2.2×10−5cm2/V-s was observed. After treatment, the sludge pH values near the anode and cathode were in the range of 6.5–7.5 and 9.5–10.8, respectively. The effectiveness of the EASD process was directly related to the magnitude of the electric current in the system. Increasing the potential gradient would enhance the extent of dewatering efficiency. As a constant electrical gradient of 1.25V/cm was applied, the moisture content of sludge decreased to 63.6% after 4-h treatment. The moisture content of sludge decreased further to 48.8% as the process operated at an applied potential gradient of 5.0V/cm. Energy requirement per unit ton of sludge treated was 17.7–86.5kWh/ton (dry weight). Preliminary cost analysis of the EASD dewatering process showed that approximately a saving of 23% sludge disposal cost could be realized. Results indicated that the EASD process is an economic, viable and effective technology in assisting sludge dewatering.

Microwave Demulsification Mechanism and Effect on Petrol Oil Sludge

In the experiments of microwave radiation sludge, the method of air floating, settlement and centrifugal separation are employed to research the demulsification effect of sludge comparative. Results show that: A perfect demulsification effect can be obtained when the radiation intensity is 2w/g, sludge PH value is 2, radiation time is 3-4min, slurry ratio is 1:3 and the oil sludge is processed by microwave.

PH dependency of hydrogen fermentation from alkali-pretreated sludge

Batch tests were carried out to study the possibility of hydrogen production from alkali-pretreated sludge without seed and the pH dependency of hydrogen fermentation from alkali-pretreated sludge. Experimental results showed that the sewage sludge with alkali-pretreatment could be successfully applied to biologically producing hydrogen without seed and extra-feed. The results also showed that the initial pH value of sewage sludge was an important factor throughout the hydrogen fermentation of alkali-pretreated sludge. The maximum hydrogen yield was obtained at initial pH value of 11.0 (14.4 mL·g VS−1). The hydrogen yield of alkali-pretreated sludge at alkaline initial pH value was much higher than that of acidic or neutral initial pH value. The optimal pH value of hydrogen production from alkali-pretreated sludge was approximately 9.5. The consumption of hydrogen could be inhibited when the pH value of sludge was above 8.5. The change of hydrogen yield at various initial pH values was similar to that of sludge SCOD. The change of sludge pH value was slow and acetate was the major component of volatile fatty acids produced in the process of hydrogen production. The yield and the constitution of volatile fatty acids were sensitive to the initial pH value.

Effect of acid and surfactant treatment on activated sludge dewatering and settling

The effect of pretreating activated sludge with sulfuric acid and surfactant on its exocellular polymer(ECP), dewaterability and settleability was investigated. It was observed that the centrifugal dewatering efficiency was increased with the decrease of sludge pH value, and which was further improved if the surfactant was simultaneously applied. However, to the filtration dewatering, the water content reached the minimum in the case of pH 2.5, and the additional use of surfactant was also favorable. The water content of sludge dewatered with filtration reached 73.99% when a pH 2.5 and a 0.1 g surfactant were employed, which was reduced by around 2% as compared with surfactant unused. Experimental results indicated that the sludge sedimentation rate was significantly accelerated under pH 2.5 condition, and which was increased once more by the utilization of surfactant. Further studies revealed that treating activated sludge with sulfuric acid at pH 2.5 or combined with surfactant was an effective method to remove the polymers from sludge surface and induced the decrease of ECP, which resulted in the improvement of dewaterability and settleability. This study suggested the potentiality of improving activated sludge mechanical dewaterability by the use of sulfuric acid to control its pH at 2.5 or together with a surfactant.

Characteristics of arsenic elution from sewage sludge

AbstractCharacteristics of arsenic elution from sewage sludge were studied at different sludge pH values to develop a removal process for arsenic in sewage sludge. Forms of arsenic compounds (arsenious acid (As(III)), arsenic acid (As(V)), monomethylarsonic acid and dimethylarsinic acid) eluted from the sludge were analyzed using high‐performance liquid chromatography–inductively, coupled plasma mass spectrometry. It was confirmed that four compounds of arsenic in the liquid phase separated from the sludge could be clearly classified and directly determined without being interfered with by coexistent matter dissolved from the sludge. An increase in sludge pH effectively increased the amount of arsenic eluted from the sludge. Although the sludge oxidation–reduction potential was increased by decreasing the sludge pH with sulfuric acid, the elution of arsenic was slight at pH 1. The predominant form of arsenic eluted from the sludge was arsenic acid at sludge pH 5, 7, 9 and 11, whereas it was arsenious acid at pH 1. Both monomethylarsonic and dimethylarsinic acids were insignificantly eluted at all of the pH values investigated. The form of arsenic dissolved from the sludge was found to almost correspond with that obtained from the Eh–pH diagram of arsenic in an aqueous system. It was concluded that elution of arsenic from sludge was promoted by increasing sludge pH and the dissolved arsenic existed mainly as arsenic acid at high pH. Copyright © 2001 John Wiley & Sons, Ltd.

Factors affecting toxic metals removal from digested sewage sludge by enriched sulphur-oxidizing microorganisms

Abstract Enriched sulphur-oxidizing microorganisms were applied to remove metals from anaerobically digested sewage sludge in laboratory reactors. The pH drop and rise in oxidation-reduction potential (ORP) of the sludge by microorganisms were mainly responsible for the metal solubilization. There was a significant effect of the sulphur amount per unit volume of sludge, the initial pH of the sludge, the inoculum size and the sludge solids concentration on the pH, the sulphate production rate, the ORP, the maximum metal solubilization rate, and the time required to achieve the acceptable level of Cu for sludge land application. The enriched microorganisms were able to grow and reduce the pH at a wide range of initial sludge pH values. Metals (Cu, Zn) were solubilized efficiently as a result of decreased pH.

Copper Activity in Soil Solution: II. Relation to Copper Accumulation in Young Snapbeans

AbstractSoil solution Cu2+ activity measured in soil saturation extracts was compared with Cu accumulation in young snapbeans (Phaseolus vulgaris L.). Copper was supplied through sewage sludge mixtures of varied Cu concentrations and through Cu‐salt additions to the soil. Treatments were a factorial combination of four levels of Cu additions and four levels of total sludge additions. Soil and sludge pH values were limited to pH 5.0 to 5.5. Plant yield differences were minor. Data are reported showing the relationships of root, shoot, and total plant Cu contents with Cu2+ activity, with DTPA‐extractable Cu, with soluble Cu, and with sludge Cu concentration. The Cu source (sludge vs. salt) produced distinctly different curves in most every case. Sludge treatments demonstrated nonlinear relationships of Cu activity vs. Cu accumulation; these were fit with exponential functions. Higher shoot Cu concentrations occurred with the Cu salt treatments. Higher root Cu levels occurred at lower Cu2+ activity values with sludge as the Cu source. This probably reflects the superior ability of the sludge to replenish or maintain the Cu supply in soil solution. Total soluble Cu was not related to plant Cu. The proportion of Cu in the sludge was closely linked with shoot Cu (r2 = 0.94); root Cu levels also reflected the proportion of Cu in the sludge, but higher sludge rates resulted in increased root Cu. Increased labile, soluble, Cu‐organic complexes with increased sludge rates would explain both the observed differences between salt and sludge treatments and the positive correlation of root Cu and sludge rate. Physiological control of Cu translocation within the plant is implicit in this reasoning. Continual monitoring of soil solution ion activity or a buffering index is needed to improve predictions of plant ion uptake.