Rich Sludge Research Articles

Insight into direct phosphorus release from simulated wastewater ferric sludge: Influence of physiochemical factors

Phosphorous recovery from chemical phosphorus removal (CPR) plants is limited. CPR plants that use iron salts for phosphorous removal generate iron phosphate (Fe-P) rich sludge. This study investigates the influence of pH and competing anions (chloride), on phosphorus and soluble iron release from lab simulated Fe-P sludge. Factors influencing recovery, such as sludge age and Fe/P molar ratio are also investigated. Results showed that alkaline treatment of Fe-P sludge was not effective in releasing Fe (<3%) but effective in releasing P, particularly at controlled pH value of 10 where the %P release was (90 ± 2%). Sludge ageing time did not affect P release from Fe-P sludge at ages less than 5 days. However, a remarkable decrease in %P release (i.e., 50% reduction) was observed at ages of 9 and 11 days for pH values of 9–10. Arsenic extraction of exchangeable surface bound P from Fe-P sludge and surface area determination of hydrous ferric oxide (HFO) under different aging times supported qualitatively the internalization of surface bound P during aging, which is a proposed mechanism responsible for the decrease in P release for older sludge. Chloride effect in releasing P from Fe-P sludge was negligible. The reduction in P release by aging was best described by a zero-order kinetic model. Modeling with the PHREEQC geochemical software did not always agree with the measured release of phosphorus from the Fe-P sludge. PHREEQC assumes all surface sites for phosphorus are exchangeable and has no mechanism to represent phosphorus trapped within HFO particles.

Vitrification of Iron Oxide Rich Sludge Resulted from the Groundwater Treatment as New Glass Ceramic Materials

This paper offers a new solution to vitrify the sludge resulted from washing the filters used for iron removal phase of the groundwater treatment process. The new glass ceramic materials, obtained after heat treatment at three different temperatures: 800, 900 and 1000 oC were characterized in terms of dimensional stability after firing, apparent density and porosity, hydrolytic stability and iron ions immobilization capacity. The effect of the calcined sludge amount upon the mentioned properties was analysed.&#x0D;

Pozzolanic reactivity of aluminum-rich sewage sludge ash: Influence of calcination process and effect of calcination products on cement hydration

The application of aluminum-based flocculant in wastewater treatment results in a large amount of aluminum-rich sewage sludge. This work investigated the influence of calcination process on physicochemical characteristics and pozzolanic activity of aluminum (Al)-rich sludge ash and studied the effect of sludge ash on cement hydration. The results showed that higher calcination temperature from 600 ℃ to 900 ℃ increased the amorphous content in sludge ash. The pozzolanic activity of sludge ash calcined at 800 ℃ and 900 ℃ was confirmed by Frattini test. In view of strength activity index of blended mortar and energy conservation, the optimal calcination condition of sewage sludge ash was calcined at 800 ℃ with air-cooling. The addition of sludge ash promoted the transformation of ettringite to monosulfate phase in cement paste. However, the high Al concentration dissolved from S6 and S7 ash inhibited significantly the cement hydration and resulted in low compressive strength values of the blended mortars. The pozzolanic reaction of S8 and S9 ash produced more hydration heat and additional Al-bearing products such as katoite and monosulfate which contributed to the strength development of mortars. Furthermore, the heavy metals in sewage sludge can be immobilized in ash structure during calcination process and the structure of hydration products, which ensures the environmental security of sludge ash utilization in construction materials.

Effect of surfactants on phosphorus release and acidogenic fermentation of waste activated sludge containing different aluminium phosphate forms

The effects of different surfactants (rhamnolipid, trehalolipid and citrate) on phosphorus (P) release and acidogenic fermentation of waste activated sludge (WAS) containing different aluminium phosphate forms (AlPO4, Al(PO3)3) were investigated. Results showed that rhamnolipid was the most effective surfactant to release P from aluminum phosphates (AlPs)-rich sludge. Al(PO3)3 was easier to release P than AlPO4 in WAS due to their different crystal structures. Different surfactants promoted the production of different types of protein. The addition of rhamnolipid was conducive to produce propionate from WAS, while trehalolipid and citrate increased the production of n-butyrate and acetate, respectively. Citrobacter played an important role in producing phosphatase continuously for P release with rhamnolipid addition. Predictive functional profiling indicates that rhamnolipid greatly facilitated adenosine triphosphate (ATP)-binding cassette transporter and quorum sensing. These important discoveries help to enrich P recovery paths from sludge produced with Al-based coagulants in wastewater treatment plants.

Biochar application in organics and ultra-violet quenching substances removal from sludge dewatering leachate for algae production

Algae production in nutrient rich sludge dewatering leachate after biogas production is a promising option for wastewater treatment plants. However, the ultra-violet (UV) absorbing characteristic of UV-quenching substances (UVQS) existing in these waters can notably reduce the light transmission within the liquid body. The present work demonstrates a comparative adsorptive removal of UVQS, and other organic substances (expressed as COD and TOC) onto the “acid catalyst” functionalised adsorbent (PPhA) and commercial activated carbon (CAC) from leachate originating from leftover sludge dewatering after biogas production. Laboratory scale column studies were performed to investigate the adsorption performance of selected parameters. The PPhA increased the UV transmittance of leachate more than 4 times and outperformed CAC. Bed Depth Service Time and Yan models were used on the experimental data in order to estimate the maximum adsorption capacity and evaluate the characteristics of the fixed-bed. The PPhA equilibrium uptake of COD and TOC amounted to 5.7 mg/g and 0.9 mg/g, respectively. The postulated removal mechanism in environmentally relevant conditions (e.g., pH neutral) suggested a complex interaction between the biochar and organic macromolecules. Diluted phosphoric acid solution (0.01 mol/L) was successfully used for the column regeneration. Beside the UVQS, PPhA showed affinity towards toxic heavy metals (e.g., Pb, Ni, Co) pointing out the rich surface chemistry of the PPhA. Based on the obtained results and successfully implemented scale-up methodology, the low-cost PPhA adsorbent might effectively compete with the CAC as a highly efficient platform in wastewaters leachate processing.

A Sustainable Solution to Obtain P-K-Mn Glass Fertilizers from Cheap and Readily Available Wastes.

The sustainable economy framework imposes the adoption of new ways for waste reuse and recycling. In this context, this paper proposes a new alternative to obtain glass fertilizers (agriglasses) by reusing two cheap and easily available wastes, wood ash and manganese rich sludge resulting from drinking water treatment processes for groundwater sources. Glasses were obtained using different amounts of wastes together with (NH4)2HPO4 and K2CO3 as raw materials. The P-K-Mn nutrient solubilization from the obtained glasses was investigated using a citric acid solution. The kinetics of the leaching process was studied after 1, 7, 14, 21 and 28 days, respectively. The intraparticle diffusion model was used to interpret kinetic data. Two distinct stages of the ion leaching process were recorded for all of the studied compositions: first through intraparticle diffusion (the rate-controlling stage) and second through diffusion through the particle–medium interface. The fertilization effect of the obtained agriglasses was studied on a barley crop. The specific plant growth parameters of germination percentage, average plant height, biomass and relative growth rate were determinate. The positive impact of the agriglasses upon the plants biomass and relative growth rate was highlighted. The effects of agriglasses can be tuned through glass compositions that affect the solubility of the nutrients.

Achieving synergetic treatment of sludge supernatant, waste activated sludge and secondary effluent for wastewater treatment plants (WWTPs) sustainable development

A novel process that combines partial nitrification, fermentation and Anammox-partial denitrification (NFAD) was proposed to co-treat ammonia rich sludge supernatant (NH4+-N = 1194.1 mg/L), external WAS (MLSS = 22092.6 mg/L) and WWTP secondary effluent (NO3–-N = 58.6 mg/L). Three separated reactors were used for partial nitrification (PN-SBR), integrated fermentation and denitrification (IFD-SBR) and combined Anammox-partial denitrification (AD-UASB), respectively. The process resulted in excellent nitrogen removal efficiency (NRE) of 98.7%, external sludge reduction efficiency (SRE) of 44.6% and external sludge reduction rate of 4.1 kg/m3 after 200 days of continuous operation. IFD-SBR and AD-UASB contributed towards 89.4% and 9.2% nitrogen removal, respectively. In AD-UASB, cooperation between Anammox bacteria (4.1% Candidatus Brocadia) and partial denitrifying bacteria (3.2% Thauera) resulted in significant stability of Anammox pathway, which contributed up to 84.1% nitrogen removal in the combined Anammox-partial denitrification process. NFAD saved up to 100% organic resource demand and 25% of aeration consumption compared with the traditional nitrification–denitrification process.

Biochar prepared from Fe‐rich sludge as suitable microbial carriers for facilitating biodegradation of phenanthrene in soil

AbstractBACKGROUNDConverting waste biomass to biochar by pyrolysis is increasingly recognized as an effective waste regeneration method and could be applied in contaminated soil bioremediation. In this work, we compared the properties of three biochars (FB300, FB500 and FB700) derived from iron (Fe)‐rich sludge (FS) at 300, 500 and 700 °C, and selected FB500 as microbial carrier to evaluate its function in facilitating phenanthrene (PHE) biodegradation in soil.RESULTSIncreasing pyrolysis temperature induced a positive relationship with the ash content, pH and pore size of biochars, but a negative relationship with the yield and surface area of the biochars. FB300 and FB500 maintained more organic matter than FB700, whereas, FB500 and FB700 had greater aromatic constituents and more crystal structures than FB300. Besides, FB500 showed the strongest stability and unique magnetic properties. Thus, FB500 was selected as microbial carrier in facilitating PHE biodegradation in soil. The degradation results indicated that FB500 with bacteria immobilization played a significant role in PHE degradation; its PHE removal rate of 58.15 ± 4.90% was much higher than that of 38.73 ± 3.98% for free bacteria treatment on the first day of degradation.CONCLUSIONFe‐rich sludge can be efficiently converted into biochar that in turn can serve as microbial carrier for PHE biodegradation in contaminated soil. FB500 with bacteria immobilization was proven to promote PHE degradation. Pyrolyzing Fe‐rich sludge to biochar is a promising method for remediation of PAH‐contaminated soil. © 2021 Society of Chemical Industry (SCI).

Differing Phosphorus Crop Availability of Aluminium and Calcium Precipitated Dairy Processing Sludge Potential Recycled Alternatives to Mineral Phosphorus Fertiliser

The European dairy industry generates large volumes of wastewater from milk and dairy food processing. Removal of phosphorus (P) by complexing with metal (e.g., aluminium, calcium) cations in P rich sludge is a potential P source for agricultural reuse and P recycling. However, there is a significant knowledge gap concerning the plant availability of this complexed P in comparison to conventional mineral P fertiliser. The current absence of information on plant P bioavailability of dairy processing sludge (DPS) limits the ability of farmers and nutrient management advisors to incorporate it correctly into fertiliser programmes. The present study examined the most common types of dairy sludge—(1) aluminium-precipitated sludge (“Al-DPS”) and (2) calcium-precipitated lime-stabilised sludge (“Ca-DPS”) at field scale to assess P availability in grassland versus mineral P fertiliser over a growing season. The experimental design was a randomised complete block with five replications. Crop yield and P uptake were assessed for 4 harvests. The initial soil test P was at a low level and the experimental treatments were super phosphate at 15, 30, 40, 50 and 60 kg P ha−1, two dairy sludge applied at 40 kg P ha−1 (comparison was made with mineral P at same application rate) and a zero P control applied in a single application at the beginning of the growing season. Results showed a significant positive slope in the relationship between P uptake response and mineral P application rate indicating the suitability of the experimental site for P availability assessment. The P bioavailability of Al- and Ca-DPS varied greatly between treatments. The P fertiliser replacement value based on the 1st harvest was 50 and 16% increased to 109 and 31% cumulatively over the four harvests for Al- and Ca-DPS, respectively. The Al concentration in Al-DPS did not limit P bioavailability, but low P bioavailability from Ca-DPS can be associated with its high Ca content that can lead to formation of low soluble Ca-P compounds at alkaline pH conditions with a high Ca/P ratio. These findings show that P availability from dairy sludge can be quite different depending on treatment process. Consequently, it is critical to have P availability information as well as total P content available to ensure the application rate meets crop requirements without creating environmental risk by over application.

Phosphorus recovery from the liquid phase of anaerobic digestate using biochar derived from iron−rich sludge: A potential phosphorus fertilizer

A novel technique for phosphorus recovery from the liquid phase of anaerobic digestate was developed using biochar derived from iron−rich sludge (dewatered sludge conditioned with Fenton’s reagent). The biochar pyrolyzed from iron−rich sludge at a low temperature of 300 °C (referred to as Fe−300 biochar) showed a better phosphorus (P) adsorption capacity (most of orthophosphate and pyrophosphate) than biochars pyrolyzed at other higher temperatures of 500–900 °C, with the maximum P adsorption capacity of up to 1.843 mg g−1 for the liquid phase of anaerobic digestate. Adsorption isotherms study indicated that 70% P was precipitated through chemical reaction with Fe elements, i.e., Fe(II) and Fe(III) existed on the surface of the Fe−300 biochar, and other 30% was through surface physical adsorption as simulated by a dual Langmuir-Langmuir model using the potassium dihydrogen orthophosphate (KH2PO4) as a model solution. The seed germination rate was increased up to 92% with the addition of Fe−300 biochar after adsorbing most of P, compared with 66% without the addition of biochar. Moreover, P adsorbed by the chemical reaction in form of iron hydrogen phosphate can be solubilized by a phosphate-solubilizing microorganism of Pseudomonas aeruginosa, with the total solubilized P amount of 3.045 mg g−1 at the end of an incubation of 20 days. This study indicated that the iron−rich sludge−derived biochar could be used as a novel and beneficial functional material for P recovery from the liquid phase of anaerobic digestate. The recovered P with biochar can be re-utilized in garden soil as an efficient P−fertilizer, thus increasing the added values of both the liquid phase of anaerobic digestate and the iron−rich sludge.

Characterisation and utilization of steel industry waste sludge as heterogeneous catalyst for the abatement of chlorinated organics by advanced oxidation processes.

Catalytic advanced oxidation processes (AOPs) utilising UV irradiation have been reported to be highly efficient for the degradation of recalcitrant compounds. The focus of present study was to evaluate the potential of steel industry waste as an alternative to homogenous iron salts often used in AOPs. Iron rich sludge from effluent treatment plant (ETP) of a steel industry was subjected to acid washing and acid washing followed by calcination before using as catalyst for the oxidative removal of chlorinated organics present in synthetic and simulated bleaching effluents. The maximum total organic carbon removals of 64% and 25% from 4-chlorophenol solution and simulated pulp bleaching effluent, respectively were observed during photo-catalytic oxidation with acid washed steel sludge at stoichiometric H2O2 dose after 2 h reaction (catalyst dose = 1 g/L, and pH = 4.4). Low iron leaching (<2%) was observed from the catalyst even in acidic conditions and it could be reused twice without significant loss of catalytic activity.

Conflicting carbon footprint and energy saving in a side-stream Anammox Process

In the last decade, policies exclusively based on reducing the electricity consumption have pushed for the use of more energy efficient processes, such as anammox-based processes for biological nitrogen removal from wastewater. In this study, a pilot-scale Anammox reactor has been incorporated into an optimized full-scale wastewater treatment plant. The supernatant of the reject sludge waters has been treated by the full scale wastewater treatment plant with and without incorporating a full-scale Anammox reactor in the sludge line. Energy consumption and nitrous oxide emissions have been monitored in both scenarios.In terms of total impact, a side-stream Anammox process can effectively mitigate the nitrogen rich sludge reject water. The impact on the carbon footprint of the full-scale wastewater treatment plant is instead, to its best, neutral. The risks related to the incorporation of an Anammox process have been highlighted: if operations are not bound to good practices, they may lead to a severe increase in carbon footprint. The use of side-stream technologies, that can further reduce both electricity consumption and the total impact but not the carbon footprint, remains attractive only when good practices for nitrous oxide mitigation are enforced.

Enhancement of Sewage Sludge Bioconversion to Methane by the Addition of Exhausted Coffee Biowaste Liquid Fraction

Anaerobic co-digestion of organic rich wastes and wastewater sludge has become an attractive economic possibility for water utilities as it enhances biogas production. The suitability of the organic rich waste depends on its biodegradability as well as on its synergetic effect on the anaerobic digestion process. The feasibility of sewage sludge (SS) treatment via co-digestion was studied in a semi-continuous mode at mesophilic conditions (36 ± 1 °C), with a hydraulic retention time of 17 days and an average organic loading rate of 0.94 ± 0.05 gVS Lreactor day−1, using the liquid fraction of pre-treated exhausted coffee biowaste (LECB) as a co-substrate. An anaerobic co-digestion trial (T1) was performed using as feeding mixture 80% SS and 20% LECB (v:v) and compared against a reference scenario of mono-digestion of SS (T0). The stability along assays was ensured by monitoring the digestate characteristics (pH, electrical conductivity, total alkalinity and ammonia content) and the specific energy-loading rate (SELR). Along the operation time of T1, methane yield and VS removal were significantly higher in comparison to mono-digestion of SS. Results showed that the addition of the co-substrate had a positive effect on specific methane production (3 times higher) and methane content (12% higher), indicating this is a feasible strategy towards self-sufficient wastewater treatment plants.

Research on lateral flow treatment technology to enhance phosphorus removal of AAO process

Removing efficiently and recycling of phosphorus in the wastewater, was not only an effective means to prevent and cure the eutrophication of water, but also an important way to realize the recovery of phosphorus resources. In the traditional AAO process, the discharge of phosphorus rich sludge could reach the goal of phosphorus removal. However, the treatment of phosphorus rich sludge was difficult and could not achieve the goal of phosphorus recovery. The lateral flow phosphorus removal treatment technology, building on the side of the traditional AAO system, was an efficient process to realize high efficiency phosphorus removal and phosphorus resources recovery by forming phosphate precipitation or crystallization. In this paper, by summarizing and analyzing the existing technology of lateral flow phosphorus recovery wastewater treatment based on AAO mainstream technology, the future development of this technology was also prospected.

Red mud as a substitute coloring agent for the hematite pigment

Red mud (RM), a highly alkaline iron oxide rich sludge obtained during the production of alumina, was treated to work as a coloring agent for ceramic glazes. The approach aims the valorization of this residue, adding environmental and economic value. RM was sintered at different temperatures (1100°C, 1150°C, 1200°C, 1250°C, 1300°C and 1350°C) to assess changes in its mineralogical composition. The obtained powders were characterized by XRD, UV–Vis and CIELab. The samples were added to glazes (transparent, opaque and matte) and their color stability analyzed by CIELab. RM sintered at 1300°C was compared with commercial hematite producing lower coloring power but yielding better color stability on glazes for temperatures of 1100°C ± 15°C, thus presenting RM_1300C as a suitable substitute for the hematite pigment.

Encouraging “K” strategy nitrifiers over “r” strategists in bioaugmentation reactor

Bacteria responsible for ammonia oxidization (AOB) can be differed into two groups which have different bio kinetic parameters. Those groups are slow growing bacteria with lower half saturation coefficient for NH4 (k -strategist) and fast growing bacteria with higher half saturation coefficient for NH4 (r- strategist). By controlling operational conditions of process it is possible to create dominance of one of those colonies to enhance the nitrification rate. Therefore model of sequencing bath reactor was developed to study the correlation of bioaugmentation of the side stream breeder reactor and predominant AOB culture. The course of the study was to find the minimal bioaugmentation influent of AOB rich recycled sludge to create dominance of k-strategist in the side stream reactor with maintaining maximal possible increase of overall AOB load. In addition operating conditions like sludge retention time, NH4 concentration and loading regimes was investigated to determine the optimum for the process.

Wastewater Biosolid Composting Optimization Based on UV-VNIR Spectroscopy Monitoring.

Conventional wastewater treatment generates large amounts of organic matter–rich sludge that requires adequate treatment to avoid public health and environmental problems. The mixture of wastewater sludge and some bulking agents produces a biosolid to be composted at adequate composting facilities. The composting process is chemically and microbiologically complex and requires an adequate aeration of the biosolid (e.g., with a turner machine) for proper maturation of the compost. Adequate (near) real-time monitoring of the compost maturity process is highly difficult and the operation of composting facilities is not as automatized as other industrial processes. Spectroscopic analysis of compost samples has been successfully employed for compost maturity assessment but the preparation of the solid compost samples is difficult and time-consuming. This manuscript presents a methodology based on a combination of a less time-consuming compost sample preparation and ultraviolet, visible and short-wave near-infrared spectroscopy. Spectroscopic measurements were performed with liquid compost extract instead of solid compost samples. Partial least square (PLS) models were developed to quantify chemical fractions commonly employed for compost maturity assessment. Effective regression models were obtained for total organic matter (residual predictive deviation—RPD = 2.68), humification ratio (RPD = 2.23), total exchangeable carbon (RPD = 2.07) and total organic carbon (RPD = 1.66) with a modular and cost-effective visible and near infrared (VNIR) spectroradiometer. This combination of a less time-consuming compost sample preparation with a versatile sensor system provides an easy-to-implement, efficient and cost-effective protocol for compost maturity assessment and near-real-time monitoring.

Physicochemical characteristics of cementitious building materials derived from industrial solid wastes

In this study the possibility of using alternative waste materials with cementitious properties was studied. Lime rich sludge (LRS) (solid waste of acetylene industry), ground granulated blastfurnace slag (GGBFS) and fine kaolinite sand (FKS) (by-product during kaolin mineralization) were used in the production of cementitious building materials. Different mixes were prepared using percentage weight ratios 80/20, 75/25, 70/30 of GGBFS and LRS, respectively, at water/cement ratio of 0.20 by weight. Fine kaolinite sand (5wt%) was used as addition in these mixes. The mechanical and hydration characteristics of the prepared pastes were studied at various time intervals up to 90days. The results showed that LRS acts as an alkaline activator for GGBFS and the optimum mix composition for activation was 75% GGBFS and 25% LRS. Addition of fine kaolinite sand (FKS) to these mixes resulted in a marked improvement in the hydraulic properties especially in the early hydration ages; this is related to the higher rate of pazzolanic interaction between the lime in LRS and the aluminosilicate constituents in fine kaolinite sand leading to formation of excessive amounts of calcium silicate hydrates (CSH) which act as binding centers between the remaining unhydrated parts of GGBFS and FKS. XRD patterns and DSC thermograms obtained for all pastes showed that the main hydration products are nearly amorphous and microcrystalline calcium silicate hydrates as well as minor amounts of calcium aluminosilicate hydrates.

Conversion of Fe-rich waste sludge into nano-flake Fe-SC hybrid Fenton-like catalyst for degradation of AOII

Permanently increasing in the amount of sludge resulted in the serious environment burden. This work reports a novel carbothermal process for converting the Fe-rich waste sludge into cleaner nano-flake Fenton-like catalyst to relieve the crisis. The transformation of Fe species at different carbothermal temperature was evaluated by XRD analysis. SEM and XPS analyses were involved to characterize the morphology and chemical bonds of the catalysts. Results shown that the resulted catalyst carbonized at 800 °C (Fe-SC-800) was composed of Fe0 and Fe3O4, performing nano-flake-like structure. The Fe-SC-800 has the highest catalytic activity in degradation of AOII in C0 = 200 mg/L. The efficiency achieves at 98% within 30 min at neutral pH, which is ascribed to the hydroxyl radical oxidation. Moreover, no iron is leached and the Fe-SC-800 could be recycled for three times at least. Thus, the Fe rich sludge could be reutilized as a valuable source for eco-friendly catalyst production, constituting an ecological way to manage these sludge wastes and eliminate the sludge and organic pollution to environment.

Ecotoxicity of arsenic contaminated sludge after mixing with soils and addition into composting and vermicomposting processes

Sludge coming from remediation of groundwater contaminated by industry is usually managed as hazardous waste despite it might be considered for further processing as a source of nutrients. The ecotoxicity of phosphorus rich sludge contaminated with arsenic was evaluated after mixing with soil and cultivation with Sinapis alba, and supplementation into composting and vermicomposting processes. The Enchytraeus crypticus and Folsomia candida reproduction tests and the Lactuca sativa root growth test were used. Invertebrate bioassays reacted sensitively to arsenic presence in soil-sludge mixtures. The root elongation of L. sativa was not sensitive and showed variable results. In general, the relationship between invertebrate tests results and arsenic mobile concentration was indicated in majority endpoints. Nevertheless, significant portion of the results still cannot be satisfactorily explained by As chemistry data. Composted and vermicomposted sludge mixtures showed surprisingly high toxicity on all three tested organisms despite the decrease in arsenic mobility, probably due to toxic metabolites of bacteria and earthworms produced during these processes. The results from the study indicated the inability of chemical methods to predict the effects of complex mixtures on living organisms with respect to ecotoxicity bioassays.