Residual Sludge Research Articles

Study on Production of Polyhydroxyalkanoates (PHAs) by Bacterial Consortium from Excess Sludge

In this experiment, the synthesis of PHAs is studied by the microbial flora in the activated sludge, the aim is to reduce the production cost of PHAs and realize the reduction and resource recovery of residual sludge. The remaining sludge from this experiment was taken from the second sink of Lizhigou sewage purification plant, the PHAs was synthesized by using glucose and sodium acetate as carbon source culture and acclimatization sludge. Under normal temperature, the control PH was between 6.9 and 8.4, and COD was in the first stage: N: P=100:5:1, continuous cultivation of 7-15d, and the second stage controlled COD: N: P=200:10:2. By regulating COD, the accumulation of PHAs reached 7.24% when COD=1000. By controlling the time of N source and P source respectively, it is found that the synthesis quantity of PHAs increased with the control time, up to 4.03% and 5.01%. The experiment is also found that the higher the C/P ratio, the greater the synthesis amount of PHAs, which can reach to 6.53%, but the sludge is easy to expand at this time.

Catalyst Based on Sludge Derived from Wastewater Treatment of Textile Industry

Study of the catalytic properties of residual sludge from effluent treatment plants of two textile industries -located in Quito Ecuador- with different dye finishing processes. The sludges were firstly dried at 110, 125 and 140°C to analyze the effect of the temperature on the mechanical strength, then they were calcined at 300, 600 and 900°C to verify the influence of the calcination temperature on the surface properties. The structural characterization was performed with: elemental analysis, infrared spectroscopy FTIR, nitrogen adsorption, X-ray diffraction, programmed temperature reduction TPR and SEM images. The catalytic properties were studied with a thermal decomposition of glycerol and different types of oil. It is concluded that the best conditions to obtain a catalytic material from these residual sludges, were: 110°C and 600°C for drying and calcination, respectively. The catalyst with a specific area of 31.73 m2/g and presence of Cr2+ and Zn0, provided higher weight loss in the thermal decomposition reaction for glycerol and the catalyst with the specific area of 30.36 m2/g and a metallic content of Fe0 promotes higher decomposition for heavy hydrocarbons. Due to the metallic content, and the physisorption and chemisorptions capability the residual sludges of textiles industries have catalytic activity and can be used for hydrocarbon decomposition.

Application of sewage sludge of shrimp farms as an alternative to organic fertilizers in the cultivation of maize (Zea mays L) in the area of Maracaibo Lake (Venezuela)

Objective: The effect of residual sludge of industrial shrimp farming on the initial growth of maize is conducted. Materials and Methods: We used bags of 5 kg with polystirene surface horizon + mud-cattle manure (L+Mo). We used an experimental design totally at random with four treatments: T1: 0% (50 kg ha -1 CV + 0 ton.ha -1 L+ Mo + complete formula 14-14-14), T2: 2% (49 kg ha-1 HP+52 ton ha-1 L + Mo) T3: 4% (48 kg ha-1 CV ton.ha-1 139-141 Cromwell Road L+Mo) and T4: 6% (47 kg ha-1 CV+156 ton ha-1 L + Mo) and 10 repetitions. Results: Non-destructive variables were evaluated (plant height, number of sheeths, the stem thickness, average length of the leaves and average width of the leaves) using repeated measures in time with five weekly evaluations and destructive variables (leaf area, dry mass and air and root) using a 4x2 factorial, with 4 treatments and 2 evaluations (21 and 35 days after sowing). In the first evaluation (21 days after) no differences were observed between treatments; while for the second evaluation (35 days after) the T4 with the dose of 156 ton.ha-1L + MO showed the greatest growth of maize during under controlled conditions. Applications: The incorporation of sludge produced improvements in physical and chemical properties of the soil recipient. Keywords: Cultivation of Zea mays L, Organic Fertilizers, Sewage Sludge, Shrimp Farms

Bio-oil production using residual sewage sludge after lipid and carbohydrate extraction

Bio-oil production using residual sewage sludge after lipid and carbohydrate extraction

Mesophilic anaerobic co-digestion of residual sludge with different lignocellulosic wastes in the batch digester

Co-digestion of residual sludge (RS) and different lignocellulosic wastes (LWs) including greening waste (GW), decocted Chinese herbs waste (DCHW) and sugarcane bagasse waste (SCBW) was investigated in batch digester. Results show that the application of GW presented the highest specific methane yield (161 mL CH4/g VSadded) due to its high carbohydrate fraction and more balanced C/N ratio in co-substrate mixture. Buswell equation was applied and it is found that biodegradability index (BI) for co-digestion varied from 68.1% to 74.2% (53.0% for RS mono-digestion) depending on the lignin fractions of the LWs. Variation of pH, VFAs, alkalinity and ammonia throughout the digestion were also examined. The addition of LWs induced VFAs formation, as well as their conversion to methane. The higher microbial diversity in RS/LWs co-digestion further confirmed the positive effect of LWs addition in co-digestion.

Effect of crystal size on zinc stabilization in aluminum-rich ceramic matrix

With aluminum as the predominant element, incineration residues from municipal solid waste and sewage sludge may be reused as precursors for zinc stabilization. As solid-state reactions are influenced by the crystal sizes of the reactants, the aluminum-containing components with different crystal sizes in the incineration residues may affect zinc transformation and immobilization. In this study, Al2O3 was prepared with a variety of crystal sizes to simulate the aluminum-rich incineration residue matrix, and ZnO was mixed with Al2O3 to study the zinc incorporation mechanisms. The crystal sizes of Al2O3 were determined using Rietveld refinement. Quantification results showed that ~ 30% of zinc was incorporated into the ZnAl2O4 spinel when Al2O3 with the largest crystal size was used. However, the zinc transformation was enhanced twofold when the Al2O3 precursor had the smallest crystal size. This study confirmed the potential enhancement of zinc immobilization by nanoscale crystals in simulated aluminum-rich incineration residues. By improving zinc stabilization efficiencies using poorly crystallized aluminum-containing compounds instead of increasing the energy consumption by increasing the sintering temperatures, we can achieve an economic and environmental win–win scenario for the beneficial utilization of incineration residues of municipal solid waste and sewage sludge.

Radical assisted iron impregnation on preparing sewage sludge derived Fe/carbon as highly stable catalyst for heterogeneous Fenton reaction

Radical induced sewage sludge pretreatment has been developed to enhance sludge stabilization and dewaterability. Except for anaerobic digestion, the reutilization of the oxidized sludge residuals is still a challenging issue for wastewater treatment plant. In the view of favorable role in sludge disintegration, the pretreated sludge precursors, which was obtained by sequential radical oxidation and iron impregnation, was carbonized to prepare the carbon encapsulated Fe nanoparticles (Fe NPs), which could then behave as highly stable and active heterogeneous Fenton-like catalyst to degrade Black-T. By contrast, the carbonized products derived from direct iron impregnation were also prepared as a control method. The effect of H2O2/Fe2+ on zeta potential, particle size, morphology and texture structure of the pretreated sludge precursors and their corresponding influence on the carbonized materials were systematically evaluated. Results showed that radicals’ activation could facilitate the iron impregnation on sewage sludge by rupturing the microbial aggregate and making them more accessible to subsequent microbial fragments. Compared to direct iron impregnation, the carbonized products featured much higher iron insertion rate and the uniformly dispersed Fe NPs encapsulated into porous carbons, which in turn enables catalysts exhibiting more efficient catalytic activity in continuous heterogeneous Fenton-like degradation and resistance to metal leaching.

Study on Adsorption of Cu2+ in WasteWater by Residual Sludge as Adsorbent

Utilizing residual sludge as adsorbent to treat Cu2+ in wastewater, The effects of pH, concentration, sludge dosage, temperature and adsorption time on Cu2+ adsorption were studied. The results was showed that removal rate of Cu2+ was better using residual sludge adsorbent to adsorb wastewater containing 20 mg/L Cu2+ when adsorption time was 3h, pH was 6∼7, temperature was 20 °C and sludge dosage was 2.0 g/L.

Supernatant organics from anaerobic digestion after thermal hydrolysis cause direct and/or diffusional activity loss for nitritation and anammox

Treatment of sewage sludge with a thermal hydrolysis process (THP) followed by anaerobic digestion (AD) enables to boost biogas production and minimize residual sludge volumes. However, the reject water can cause inhibition to aerobic and anoxic ammonium-oxidizing bacteria (AerAOB & AnAOB), the two key microbial groups involved in the deammonification process. Firstly, a detailed investigation elucidated the impact of different organic fractions present in THP-AD return liquor on AerAOB and AnAOB activity. For AnAOB, soluble compounds linked to THP conditions and AD performance caused the main inhibition. Direct inhibition by dissolved organics was also observed for AerAOB, but could be overcome by treating the filtrate with extended aerobic or anaerobic incubation or with activated carbon. AerAOB additionally suffered from particulate and colloidal organics limiting the diffusion of substrates. This was resolved by improving the dewatering process through an optimized flocculant polymer dose and/or addition of coagulant polymer to better capture the large colloidal fraction, especially in case of unstable AD performance. Secondly, a new inhibition model for AerAOB included diffusion-limiting compounds based on the porter-equation, and achieved the best fit with the experimental data, highlighting that AerAOB were highly sensitive to large colloids. Overall, this paper for the first time provides separate identification of organic fractions within THP-AD filtrate causing differential types of inhibition. Moreover, it highlights the combined effect of the performance of THP, AD and dewatering on the downstream autotrophic nitrogen removal kinetics.

An integrated system for sewage sludge drying through solar energy and a combined heat and power unit fuelled by biogas

The main challenges of wastewater treatment plants are high-energy demand and sludge disposal. A hybrid system for sewage sludge drying is proposed in this work to face both these issues. The developed layout is based on the integration of two renewable energy sources, biogas from anaerobic digestion of sludge and solar energy in order to increase sustainability and energy self-sufficiency of the plant. Biogas is used to fuel a combined heat and power system and solar energy is exploited through a parabolic trough collector field. Electrical energy produced by the combined heat and power is used to cover the plant demand, whereas thermal energy coming from the combined heat and power unit and solar field is employed to run an anaerobic digestion process and for thermal drying of the residual sludge. The considered case study is based on data collected for an existing wastewater treatment plant. The proposed system is studied through data obtained from the scientific literature, suppliers of the considered equipment and properly developed sub-models of the various components, to assess its feasibility and the overall energy, environmental and economic performance. The system is dynamically simulated and daily, weekly and yearly results are presented. For the considered desiccant flow temperatures, the solar collector field achieves a thermal efficiency of about 56.0%, while for the combined heat and power unit it is about 44.0%, which is slightly higher than the nominal one, due to the preheating of combined heat and power unit intake air. The integration of solar energy with the combined heat and power system leads to a primary energy saving of about 14.6% with respect to the existing plant, where the sludge is not digested and neither thermally dried. The economic analysis shows that the Simple Pay Back period of the system is less than 3.40 years.

Ferrous ions reused as catalysts in Fenton-like reactions for remediation of agro-food industrial wastewater

Cassava is the most important tuberous root in tropical and subtropical regions of the world, being the third largest source of carbohydrates. The root processing is related to the production of starch, an important industrial input, which releases a highly toxic liquid wastewater due to its complex composition, which inhibits high performances of conventional effluent treatments. This study aims to evaluate Fenton-like and photo-Fenton-like reactions for treatment of cassava wastewater, reusing ferrous ions from the preliminary coagulation stage. Pre-treated cassava wastewater was submitted to oxidation in three variations of hydrogen peroxide concentrations, with more relevant analytical responses verified in color, turbidity, COD (Chemical Oxygen Demand), and acute toxicity in Artemia salina, besides the action of radicals during Fenton-like reactions. At higher peroxide concentrations, a decrease of 68% in turbidity and 70% in COD on the photo-Fenton-like system was observed, even at slow reaction rates (fastest rate constant k = 2 × 10−4 min−1). Inclusion of UV increases the viability of the Fenton-like reactions by supplementing the reaction medium with hydroxyl radicals, verified by the tert-butanol tests. The oxidation process leads to high EC50 values in 24 h of incubation in Fenton-like reactions and 48 h in photo-Fenton-like reactions. Final COD and turbidity suggests that the reuse of iron, which remains in the preliminary treatment step shows a great potential as a catalyst for Fenton-like advanced oxidation processes. Tertiary treatment can be less expensive and harmful to the environment, reducing production of residual sludge and metal content in the final effluent, which reduces polluting potential of the effluent regarding solid waste.

Effect of porcelain tile polishing residue on geopolymer cement

Abstract The polishing of ceramic tiles surface produces high amounts of residual sludge, which requires deposition in controlled landfills. However, porcelain tile polishing residue (PPR) can be used as a partial source of aluminosilicate to produce geopolymer cement. Therefore, in this work, a geopolymeric cement based on PPR and metakaolin was developed using sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) as activator solution. A 23+1 factorial design was used with three factors: PPR content (15, 30 and 45 mass % in relation to metakaolin); NaOH (5, 6 and 7 mass %) and Na2SiO3 (48, 50 and 52 mass %). After synthesis, the samples were characterized by mechanical (compressive strength, hardness and dynamic modulus) and structural analyses (XRD and FTIR). The highest compressive strength was 72 MPa, obtained at 28 days (cured at 23 °C) in the composition containing 15% of PPR and 85% metakaolin, corresponding to a chemical composition with 53% SiO2, 25% Al2O3 and 11% Na2O, relation SiO2/Al2O3 = 3.44, and a structure characterized as poly (sialate-disiloxo). The results showed that PPR can be used as an alternative source of raw material to produce geopolymer cement, while contributing to the reuse of an industrial waste.

Nanoporous MnO2 Nanoflakes Modified Carbon Cloth Material for Efficient Removal of Heavy Metal Ions in Water by Capacitive Deionization

Increasing demand for the limited resource of fresh water for the large urban populations and development of agriculture and industry draws public concern. Removal of heavy metals such as lead, cadmium, chromium and mercury is crucial in environmental improvement of water and industrial wastewater treatment. Great efforts have been made through chemical precipitation, adsorption, ion exchange, filtration and electrochemical treatment. However, a large volume of sludge residue, expensive and complex matrix materials and low efficiency are still problems that need to be improved. Capacitive deionization (CDI) is a promising energy-efficient technology for water desalination, which is easy to handle and environmentally friendly producing no secondary contaminants through the water purifying process [1]. In order to effectively remove ions, the porous electrodes with large surface area, good chemical stability, high electronic conductivity, and hydrophility are key factors in the selection of CDI materials. Highly porous carbon materials represent the typical electrodes to store the ions through surface ion adsorption/desorption, which is generally categorized as electrochemical double layer. By contrast, pseudocapacitors that consist of conducting polymers and transition metals, store more charge through redox reactions. Among the alternative candidates, the natural abundant and environmental benign MnO2 is of particular interest for research, due to its high theoretical specific capacitance and the ability to be use in mild aqueous electrolytes which expand its practical application [2-3]. MnO2 can be fabricated easily and its morphology can be controlled during simple hydrothermal growth processes. Direct growth on carbon cloth, which is an excellent flexible and conductive substrate, could enhance the regeneration and reuse property of MnO2 as an ideal CDI electrode. Porous MnO2@cabon cloth composites were prepared via a facile hydrothermal method (Figure a). The BET result showed that the average pore width is 18.2 nm. To investigate the CDI property of removing the heavy metal ions, one piece of MnO2@CC and one piece of activated carbon@graphite paper were assembled as working and counter electrodes respectively. This work confirmed the potential of using MnO2@CC as a good CDI electrode material for removal of heavy metal ions from water (Figure b). References S. Porada, R. Zhao, A. Wal, V. Presser, and P. M. Biesheuvel, Prog. Mater. Sci., 58, 1388 (2013).W. Wei, X. Cui, W. Chen, and D. G. Ivey, Chem. Soc. Rev., 40, 1697 (2011).J. Wang, F. Kang, and B. Wei, Prog. Mater. Sci., 74, 51 (2015). Figure 1

Characterization of herb residue and high ash-containing paper sludge blends from fixed bed pyrolysis

High ash-containing paper sludge which is rich in various metal oxides is employed in herb residue pyrolysis to enhance the yield of fuel gas and reduce tar yield in a drop tube fixed bed reactor. Effects of heat treatment temperature and blending ratio of paper sludge on the yields and composition of pyrolysis products (gas, tar and char) were investigated. Results indicate that paper sludge shows a significantly catalytic effect during the pyrolysis processes of herb residue, accelerating the pyrolysis reactions. The catalytic effect resulted in an increase in gas yield but a decrease in tar yield. The catalytic effect degree is affected by the paper sludge proportions, and the strongest catalytic effect of paper sludge is noted at its blending ratio of 50%. At temperature lower than 900 °C, the catalytic effect of paper sludge in the pyrolysis of herb residue promotes the formation of H2 and CO2, inhibits the formation of CH4, but shows slight influence on the formations of CO, while the formation of the four gas components was all promoted at 900 °C. SEM results of residue char show that ash particles from paper sludge adhere to the surface of the herb residue char after pyrolysis, which may promote the pyrolysis process of herb residue for more gas releasing. FT-IR results indicate that most functional groups disappear after pyrolysis. The addition of paper sludge promotes deoxidisation and aromatization reactions of hetero atoms tars, forming heavier polycyclic aromatic hydrocarbons and leading to tar yield decrease.

Geopolymer synthetized from sludge residue pretreated by the wet alkalinizing method: Compressive strength and immobilization efficiency of heavy metal

To realize the reclamation of the sludge residue, we used the sludge residue pretreated by the wet alkalinizing method to prepare geopolymer. Results showed that, when the dosage of the alkali activator, the silicate modulus of the alkali activator, and the doping amount of the pretreated sludge residue were 82.5%, 1.3 mol/mol, and 20% respectively, the compressive strength of geopolymer reached a maximum at 89.03 MPa. The preparation of geopolymer also realized a highly-efficient immobilization of the unstable-forms of copper and zinc (72.22% and 68.60%) in sludge residue, which significantly reduced the pollution risks of the leaching of heavy metals.

Isolation and Characterization of PHA-Producing Bacteria from Propylene Oxide Saponification Wastewater Residual Sludge.

A polyhydroxyalkanoate (PHA)-producing strain was isolated from propylene oxide (PO) saponification wastewater activated sludge and was identified as Brevundimonas vesicularis UJN1 through 16S rDNA sequencing and Biolog microbiological identification. Single-factor and response surface methodology experiments were used to optimize the culture medium and conditions. The optimal C/N ratio was 100/1.04, and the optimal carbon and nitrogen sources were sucrose (10g/L) and NH4Cl (0.104g/L) respectively. The optimal culture conditions consisted of initial pH of 6.7 and an incubation temperature of 33.4°C for 48h, with 15% inoculum and 100mL medium at an agitation rate of 180rpm. The PHA concentration reached 34.1% of the cell dry weight and increased three times compared with that before optimization. The only report of PHA-producing bacteria by Brevundimonas vesicularis showed that the conversion rate of PHAs using glucose as the optimal carbon source was 1.67%. In our research, the conversion rate of PHAs with sucrose as the optimal carbon source was 3.05%, and PHA production using sucrose as the carbon source was much cheaper than that using glucose as the carbon source.

Properties and Beneficial Uses of (Bio)Chars, with Special Attention to Products from Sewage Sludge Pyrolysis

Residual sludge disposal costs may constitute up to, and sometimes above, 50% of the total cost of operation of a Wastewater Treatment Plant (WWTP) and contribute approximately 40% of the total greenhouse gas (GHG) emissions associated with its operation. Traditionally, wastewater sludges are processed for: (a) reduction of total weight and volume to facilitate their transfer and subsequent treatments; (b) stabilization of contained organic material and destruction of pathogenic microorganisms, elimination of noxious odors, and reduction of putrefaction potential and, at an increasing degree; (c) value addition by developing economically viable recovery of energy and residual constituents. Among several other processes, pyrolysis of sludge biomass is being experimented with by some researchers. From the process, oil with composition not dissimilar to that of biodiesels, syngas, and a solid residue can be obtained. While the advantage of obtaining sludge-derived liquid and gaseous fuels is obvious to most, the solid residue from the process, or char (also indicated as biochar by many), may also have several useful, initially unexpected applications. Recently, the char fraction is getting attention from the scientific community due to its potential to improve agricultural soils’ productivity, remediate contaminated soils, and supposed, possible mitigation effects on climate change. This paper first discusses sludge-pyrolysis-derived char production fundamentals (including relationships between char, bio-oil, and syngas fractions in different process operating conditions, general char properties, and possible beneficial uses). Then, based on current authors’ experiments with microwave-assisted sludge pyrolysis aimed at maximization of liquid fuel extraction, evaluate specific produced char characteristics and production to define its properties and most appropriate beneficial use applications in this type of setting.

Fate of antibiotic and metal resistance genes during two-phase anaerobic digestion of residue sludge revealed by metagenomic approach.

The prevalence and persistence of antibiotic resistance genes in wastewater treatment plants (WWTPs) is of growing interest, and residual sludge is among the main sources for the release of antibiotic resistance genes (ARGs). Moreover, heavy metals concentrated in dense microbial communities of sludge could potentially favor co-selection of ARGs and metal resistance genes (MRGs). Residual sludge treatment is needed to limit the spread of resistance from WWTPs into the environment. This study aimed to explore the fate of ARGs and MRGs during thermophilic two-phase (acidogenic/methanogenic phase) anaerobic digestion by metagenomic analysis. The occurrence and abundance of mobile genetic elements were also determined based on the SEED database. Among the 27 major ARG subtypes detected in feed sludge, large reductions (> 50%) in 6 ARG subtypes were achieved by acidogenic phase (AP), while 63.0% of the ARG subtypes proliferated in the following methanogenic phase (MP). In contrast, a 2.8-fold increase in total MRG abundance was found in AP, while the total abundance during MP decreased to the same order of magnitude as in feed sludge. The distinct dynamics of ARGs and MRGs during the two-phase anaerobic digestion are noteworthy, and more specific treatments are required to limit their proliferation in the environment.

Recycling of Cr/Ni/Cu plating wastes as black ceramic pigments

The non-ferrous metal industry, such as Cr/Ni/Cu plating, produces acid sludge which is usually neutralized with lime slurry in batch processes, and the resulting waste is dewatered by vacuum filtration or filter-pressing. Dewatered sludge contains calcium sulphate (CaSO4) coming from the neutralization process, as well as transition metals (Cr, Ni and Cu), oil, grease and suspended solids. In this communication, two residual sludges from Cr/Ni/Cu plating have been dried (110 °C) and fired (1100 °C), and both dried (gray coloured) and fired powders (black coloured) have been characterized by DTA-TG, XRD and SEM-EDX techniques. XRD shows only quartz crystallization in dried samples, while NiCr2O4 chromite spinel and NiO periclase crystallize in fired powders, along with CaSO4 anhydrite and CaSiO3 wollastonite. The powders have been introduced as ceramic pigments into three different conventional glazes: a) a lead bisilicate (PbO.2SiO2) double fire frit (1000 °C), b) a double fire frit with low lead content (1000 °C), and c) a double fire frit without lead (1050 °C). Glazed samples were characterized by UV-Vis-NIR (diffuse reflectance) and CIEL∗a∗b∗ (color parameters). Dried powders induce glaze defects (pin-holing and crawling), but fired powders did not show these faults exhibiting more intense (higher L∗) and yellowish (higher b∗) black colors than the standard spinel.

Response surface methodology for the optimization of sludge solubilization by ultrasonic pre-treatment

The present study examines the optimization of the ultrasonic pre-treatment conditions with response surface experimental design in terms of sludge disintegration efficiency (solubilisation of organic components). Ultrasonic pre-treatment for the maximum solubilization with residual sludge enhanced the SCOD release. Optimization of the ultrasonic pre-treatment was conducted through a Box-Behnken design (three variables, a total of 17 experiments) to determine the effects of three independent variables (power, residence time and TS) on COD solubilization of sludge. The optimal COD was obtained at 17349.4mg/L, when the power was 534.67W, the time was 10.77, and TS was 2%, while the SE of this condition was 28792J/kg TS.