Dewatered Sewage Sludge Research Articles

Environmental performance of dewatered sewage sludge digestate utilization based on life cycle assessment.

Due to the global trend of urbanization, the amount of sewage water is increasing in cities. This calls for efficient treatment of the resulting sewage sludge. To date, in the 27 European Union member countries (EU-27), the prevailing treatment method is application on arable land. Anaerobic digestion is one of the treatment methods being increasingly used nowadays. However, the resulting digestate requires further utilization. Therefore, in this study, the environmental performance of composting, combustion, and pyrolysis options for dewatered sewage sludge digestate is evaluated based on a life cycle assessment. The results show that digestate combustion and composting performed better than pyrolysis for most of the selected impact categories. However, pyrolysis of sewage sludge is still under development, and there are, to some degree, uncertainties in the data related to this technology; thus, more information for the performance assessment of pyrolysis is still required.

Improving dewaterability of sewage sludge by inoculating acidified sludge and Fe2+: Performance and mechanisms

Bioleaching is considered to be an economical and environmentally friendly strategy for sewage sludge (SS) dewatering and heavy metal removal. Acidified sludge (AS), exhibiting strong Fe2+ oxidation capacity, was obtained by repeatedly domesticating sewage sludge with Fe2+, and was treated as a novel inoculum to enhance SS dewaterability during the bioleaching process. AS addition accelerated Fe2+ oxidation and reduced the pH from 7.57 to 2.81 because of bio-acidification and bio-oxidation. After conditioning for 48 h, the SS dewaterability improved in Fe2+-treated and AS conditioned samples; the capillary suction time (CST) and specific resistance to filtration (SRF) decreased from 157.6 s and 12.5 × 1012 m/kg of raw sludge to 40.9 s and 0.53 × 1012 m/kg. Compared with the raw sludge, the total protein content in tightly bound extracellular polymeric substances (TB-EPS) decreased by 82.5% after AS and Fe2+ treatments, while it decreased by 9.69% after treatment with only Fe2+. Three-dimensional fluorescence spectroscopy showed that the decomposition of aromatic proteins, tryptophan-like proteins, and soluble microbial products in TB-EPS contributed in improving SS dewaterability. The results of microbial diversity revealed that in addition to bioleaching microorganism Acidithiobacillus playing an important role, other acid-tolerant microorganisms such as Acidocella, Thiomonas, and Metallibacterium also contribute in improving the SS dewatering performance. The symbiotic association of the above microorganisms reduced the environmental pH and protein concentration, changed the protein composition, thus promoting the release of the bound water contained in SS.

Improvement of sewage sludge dewatering by piezoelectric effect driven directly with pressure from pressure filtration: Towards understanding piezo-dewatering mechanism

Piezoelectric effect was firstly employed to improve dewatering efficiency of sludge. It was found that the piezoelectric effect could be driven directly by the pressure of pressure filtration process, without any additional energy. This piezo-dewatering process coupled piezoelectric effect with pressure filtration could efficiently remove moisture of sludge. Under 0.6 MPa for 2 h, moisture content (MC) and weight of sludge could be reduced to 63.9% and 3.2 g from 96.7% and 50 g by the piezo-dewatering process with 0.45 g t-BaTiO3. This piezo-dewatering efficiency was much higher than that of usual conditioning-pressure filtrations using CaO, FeCl3 or polyacrylamide (PAM) as the conditioners. And the piezo-dewatering process assisted by PAM could further decrease MC and weight of the sludge to 54.9% and 2.1 g, correspondingly, which complied to the advanced dewatering requirement (MC < 60%). The favorable piezo-dewatering efficiency was contributed to the piezo-catalytic oxidation and the electric role of remnant piezo-field. The finding of this piezo-dewatering mechanism offered an inspiring look at developing the emerging dewatering technology.

Investigation of the possibilities of dewatering sewage sludge by the method of electroosmosis in order to prevent land littering

Wastewater sludge from industrial enterprises is disposed of at disposal sites. This leads to a negative impact on the soil cover. The well-known methods of dehydration of moisture-containing materials have been studied. The chemical composition of sewage sludge was investigated. A technical solution for reducing the volume of wastewater sludge formation is considered on the example of cardboard and paper production. An electroosmotic installation is proposed. To study the process of sludge dewatering, a series of experiments was carried out on the installation with variable parameters of the voltage between the electrodes. A model of the particle velocity in the medium under study was presented. It has been proven that with the help of an electroosmotic device, up to 70% of moisture is effectively removed from the volume of waste sludge waste. This makes it possible to significantly reduce their volumes, reduce areas for possible or temporary placement and reduce the environmental load on the environment.

Evaluations of biochar amendment on anaerobic co-digestion of pig manure and sewage sludge: waste-to-methane conversion, microbial community, and antibiotic resistance genes

Effects of biochar on co-digestion of pig manure and dewatered sewage sludge under different total solids (TS) were investigated. Biochar could accelerate the start-up of methanogenesis and shorten the adaptation phase. At TS5%, the methane daily production in biochar group was 60.6% higher than the control; nevertheless, when TS increased, the gap between two groups gradually narrowed. Additionally, the change on antibiotics resistance genes (ARGs) was also affected by TS and the biochar addition. Moreover, biochar was beneficial to reduce ARGs in liquid phase. At TS14%, the total ARGs abundance in the liquid phase of biochar group was 41.4% lower than the control, among which the reduction rates of etB(P), sul1, rpoB2, macA, mupA and mupB were more prominent. These findings could provide useful guidance for developing ARGs elimination strategy before their release into the environment.

Removal of phosphate from aqueous solution by chitosan coated and lanthanum loaded biochar derived from urban dewatered sewage sludge: adsorption mechanism and application to lab-scale columns.

A lanthanum modified sludge biochar chitosan (La-SBC-CS) microsphere was successfully synthesized by dropping sludge biochar (BC) and chitosan into a lanthanum chloride solution. Batch adsorption experiments were conducted to investigate the adsorption kinetics and isotherm. Application of continuous phosphate removal was achieved via lab-scale column reactors. The phosphate adsorption equilibrium data of the La-SBC-CS fitted well with the Freundlich isotherm, with a maximum adsorption amount of 81.54 mg p/g at 25 °C. Characterization of the adsorbent using scanning electron microscopy analysis (SEM), X-ray energy spectrum analysis (EDS), X-ray diffraction analysis (XRD) and Fourier infrared analysis (FTIR) techniques suggested that the possible adsorption mechanisms were electrostatic interaction, ligand exchange and complexation. The La-SBC-CS kept 76.37% phosphate removal efficiency after eight recycles. The results of continuous column reactor experiment demonstrated that the breakthrough time increased with an increase in adsorbent filling height, while it decreased with an increase in initial phosphate concentration or flow velocity. The Yoon model was applied to the continuous experimental data to predict breakthrough curves and determined the characteristic adsorption parameters for process design. This study indicated the potential for the practical application of La-SBC-CS in phosphate removal from wastewater.

Open-air storage with and without composting as post-treatment methods to degrade pharmaceutical residues in anaerobically digested and dewatered sewage sludge

Over a period of 12 months, the fate of three hormones, 12 antibiotics and 30 pharmaceutically active substances (PhACs) was investigated during open-air storage without and with composting of anaerobically digested and dewatered sewage sludge. The effect of oxidation conditions during storage on degradation of hormones and PhACs in the sludge biomass was also examined. Under summer and winter conditions in Uppsala County, Sweden, two field-scale sludge windrows were constructed: open-air storage of sewage sludge windrow without composting (NO-COM)) and open-air storage windrow with composting (COM). NO-COM achieved effective removal of ∑Hormones (85%) and ∑Antibiotics (95%), but lower removal of ∑PhACs (34%), during the study year. The top layers of the sludge pile had significantly lower concentrations of ∑PhACs (3100–5100 ng/g ash) than deeper layers (8000–11,000 ng/g ash). After one year of composting, the degradation in the COM windrow resulted in concentrations of ∑Hormones (<LOD), ∑Antibiotics (<LOD), while the ∑PhCAs was 5% (730 ng/g ash) of initial (13,000 ng/g ash). The half-life of substances during composting in COM was within 7–100 days for all substances except ibuprofen (156 days). The first-order degradation constant (K) was the lowest for ibuprofen (0.0045 day−1) and the highest for oxazepam (0.0805 day−1). In conclusion, composting of sludge was effective in degrading the target hormones, antibiotics, and PhACs.

Understanding the synergistic mechanism of PAM-FeCl3 for improved sludge dewaterability

Hybrid flocculant polyacrylamide-ferric chloride (PAM-FeCl3) was developed to improve the dewaterability of sewage sludge and the dewatering performance, properties of treated sludge, composition and morphology distribution of extracellular polymeric substance (EPS) were investigated. The physicochemical properties of the PAM-FeCl3 were characterized, and its effectiveness as a sludge conditioner was evaluated. The results indicated that PAM-FeCl3 conditioning was able to promote sludge dewaterability. Simultaneously, PAM-FeCl3 neutralized the negative charges on the surface of sludge particles and increased the sludge floc size. Besides, PAM-FeCl3 also formed a rough and porous floc structure that reduced sludge compressibility. Meanwhile, the exciting emission matrix analysis suggested that PAM-FeCl3 can effectively disintegrate of EPS fraction in sludge and decompose the aromatic protein-like substances as well as the humic acid-like substances in EPS. Additionally, the larger sludge floc formation, electrostatic interaction and adsorption bridging effect resulted in compression of sludge structure and the decomposition of EPS fractions and improved sludge dewatering performance.

Speciation and Ecological Risk Assessment of Heavy Metal(loid)s in the Municipal Sewage Sludge of China

To reveal the speciation and pollution status of heavy metal(loid) s (HMs) in the dewatered sewage sludge(SS) of municipal wastewater treatment plants(MWTPs) in China, SS samples were collected from 40 MWTPs located in different regions of China. The total concentrations and geochemical fractions of As, Cd, Cr, Cu, Ni, Pb, and Zn in the SS samples were analyzed. The ecological risks induced by HMs in the SS were assessed based on the toxicity characteristic leaching procedure(TCLP), risk assessment code(RAC), and potential ecological risk index(RI). The median values of HMs in SS followed the order Zn > Cu > Cr > Pb > Ni > As > Cd. The general attainment rates of HMs in SS were satisfactory(>90%). As showed a generally even distribution among all the fractions; Cd and Zn mainly existed in the reducible fraction; Cr mainly occurred in the residual fraction, followed by oxidizable and reducible fractions; Cu mainly occurred in the oxidizable fraction; Ni occurred mainly as exchangeable forms; and Pb mainly occurred in the reducible and residual fractions, with its exchangeable form being the lowest fraction. According to the RAC method, the environmental risks induced by HMs in the SS followed the order Ni > As > Zn > Cd > Cu > Cr > Pb. The ecological risk of Ni was high; Zn, As, and Cd had a medium level of risk; Cr and Cu had a low level of risk; and the risk of Pb was negligible. According to the RI method, Cd and Cu showed the highest potential ecological risk, indicating that these are the primary HM pollutants in the SS. However, if the agricultural application of SS is carried out in accordance with the national standards, the overall level of risk from soil HM pollution is considered relatively low.

Anaerobic co-digestion of various organic wastes: Kinetic modeling and synergistic impact evaluation

Anaerobic mono- and co-digestion of coffee pulp (CP), cattle manure (CM), food waste (FW) and dewatered sewage sludge (DSS), were assessed using biochemical methane potential tests. The effects of two different inocula, anaerobically digested cattle manure (ADCM) and anaerobically digested waste activated sludge (ADWAS), and five different co-feedstock ratios for CP:CM and FW:DSS (1:0, 4:1, 2:1, 4:3, and 0:1) on specific methane yields were also evaluated. Mono-digestions of both CP and FW yielded the highest methane yield compared to the co-digestion ratios examined. Furthermore, no synergistic or antagonistic effect was observed for any of the co-digestion ratios tested. Nine different kinetic models (five conventional mono-digestion models and four co-digestion models) were compared and evaluated for both mono- and co-digestion studies. For CP:CM, cone and modified Gompertz with second order equation models were the best-fit for mono- and co-digestion systems, respectively, while for FW:DSS, superimposed model showed the best-fit for all systems.

Ultrasounds Energy as an Agent of Polyelectrolyte Modification Prior to Sewage Sludge Conditioning

The presented research concerned the phenomenon of polyelectrolyte changes resulting from modification by applying the ultrasonic field. The main aim of this research was to determine the activation degree of this macromolecular chemical compound and its effect on sewage sludge subjected to conditioning and followed by dewatering. The overall goal was to investigate the potential way of reducing the dosage of chemical compounds prior to sewage sludge conditioning. The polyelectrolyte samples were sonicated with the ultrasonic disintegrator UD-20 coupled with a sandwich concentrator. The power output of the generator was 180 W and the ultrasonic field frequency was 22 kHz. To describe the geometrical characteristics of the separated phases, the following parameters were determined: surface area (AA), perimeter (LA) and non-dimensional coefficient. With reference to the obtained results, the most significant quantitative changes in shape and size of the separated phases were observed for the ultrasonic field exposure time in the range of 0 to 10 s. This was in agreement with the results observed during dewatering of the investigated sewage sludge. In view of the quantitative analysis of the structure of the polyelectrolyte subjected to the ultrasonic modification, dewatering of sewage sludge was considerably improved by the application of the presented method.

Features of sewage sludge dewatering process at the use offlocculant based on epichlorohydrinand dimethylamine

The paper presents the results of experimental studies on the use of new synthesized reagent based on epichlorohydrin(chloropropylene oxide) and dimethylamine at the mechanical sludge dewatering unit; the effect of the residual flocculant content on sludge dewatering process is determined. In particular, it was found that the use of the proposed reagent led to increase in the efficiency of settling industrial effluents at the primary settling unit up to 95%; it had a beneficial effect on further wastewater treatment at biological treatment facilities, which led to 1.5-fold decrease in the consumption of flocculant. The use of this reagent made it possible to achieve a high degree of dewatering of sewage sludge and reduce the moisture content of the formed cake from 98 to 73%. Consequently, this allowedto significantlydecrease the volume of sludge further placed in sludge collectors and to reduce the amount of land allotted for its disposal.

Overcoming organic matter limitation enables high nutrient recovery from sewage sludge reject water in a self-powered microbial nutrient recovery cell

In order to meet the global demand of fertilizers for food production, there is an urgent need to recover macronutrients (such as NH4+, PO43−, Ca2+, K+, and Mg2+) from non-conventional sources (e.g., waste streams). Sludge reject water – a by-product produced during the dewatering of anaerobically-stabilized sewage sludge – is considered an ideal feedstock for bioelectrochemical nutrient recovery due to its high nutrient content. However, its low readily available organic matter and alkalinity usually limit electric current generation, resulting in low nutrient recovery. Here, we designed and operated self-powered microbial nutrient recovery cells (MNRCs) to test whether or not the addition of high-strength livestock wastewater could improve the macronutrients recovery from sludge reject water into a liquid concentrate. MNRCs fed with sludge reject water exhibited a low current density generation of 0.98 ± 0.31 A/m3 with approximately 24 ± 2% reduction in chemical oxygen demand (COD) concentration. The NH4+ removal was only 37.1 ± 11% with an up-concentration factor of ~0.43 ± 0.15. Macronutrients recovery and up-concentration were optimized by mixing sludge reject water with livestock wastewater, which its content varied from 10 to 30%. Consequently, the current output and NH4+ up-concentration factor were remarkably increased, peaking at 14.10 ± 1.14 A/m3 and 2.19 ± 0.51, respectively, for MNRCs fed with sludge reject water:livestock wastewater = 70%:30% (v:v). Detailed analysis of the liquid concentrate revealed that it could be efficiently used as a liquid fertilizer to replace chemical fertilizers with comparable agricultural productivity at a lower cost. These results suggest that the MNRC can promote self-powered, chemical-free macronutrients recovery from sludge reject water (and other low-strength wastewater, too) by controlling the availability of organic matter in waste streams.

Conditioning of Sewage Sludge with Physical, Chemical and Dual Methods to Improve Sewage Sludge Dewatering

The paper presents the impact of different methods of sewage sludge conditioning on the improvement of sludge dewatering during pressure filtration processes. The following conditioning methods were tested for sludge preparation: sonication, addition of organic and inorganic chemicals (Zetag 8180, PIX 113 and the combined action of both substances). The research covered: physical and chemical analysis of sewage sludge, measurement of capillary suction time as an indicator of sludge dewaterability, some technical parameters of sludge pressure filtration process and the analysis of filtrate to assess the degree of contamination. The results of the research showed that the final water content of the prepared sludge decreased, while the specific filtration resistance increased. Among the tested methods the best results of sludge dewatering effects were obtained for sonicated sludge and its preparation with inorganic coagulant PIX 113. The combined effect of sonication with the addition of chemicals Zetag 8180 and PIX113 to sludge allowed for the reduction of organic substances, ammonium nitrogen and phosphates in filtrate after sludge dewatering.

Recirculation of reject water in deep-dewatering process to influent of wastewater treatment plant and dewaterability of sludge conditioned with Fe2+/H2O2, Fe2+/Ca(ClO)2, and Fe2+/Na2S2O8: From bench to pilot-scale study

Deep dewatering of sewage sludge pretreated with advanced oxidation processes (AOPs) is a strategy for efficient sludge reduction and subsequent disposal. The pretreatment and dewatering performance of sludge conditioned with three types of AOPs (Fe2+/H2O2, Fe2+/Ca(ClO)2, and Fe2+/Na2S2O8), compared with sludge conditioned with traditional conditioner (Fe3+/CaO), were investigated in both bench and pilot-scale tests. All of those conditioner systems could reduce the water content of dewatered sludge cake to below 60 wt% in bench-scale (about 16 kg raw sludge per round) and pilot-scale (approximate 800 kg raw sludge per round) diaphragm filter press dewatering. Compared with raw sludge, the deep-dewatering filtrate after different conditioning and dewatering processes had higher ammonia nitrogen (NH4+-N) and chemical oxygen demand (COD) contents due to the degradation of organic matter, and much lower total phosphorus (TP) content due to the formation of iron phosphate precipitate. A better biodegradability (i.e. higher BOD5/COD ratio) was found in the deep-dewatering filtrate of sludge conditioned with Fe2+/H2O2 (25.2 %) and Fe2+/Ca(ClO)2 (17.4 %). Most of the heavy metals (Cr, Cu, Ni, and Pb) (>79 wt%) have remained in the dewatered sludge cake, and most of the Cl element (>90 wt%) in the sludge pretreated by Fe2+/Ca(ClO)2 and Fe3+/CaO was kept in the filtrate, rather than the dewatered sludge cake. Based on the pilot-scale experimental results, if all the filtrate in the deep-dewatering process returned to the influent of WWTP, the loading ratios of TP, NH4+-N, COD in the four conditioner systems were less than 3 wt%. The above results proved that the AOPs conditioned sludge could achieve deep-dewatering in pilot-scale and the direct recirculation of deep-dewatering filtrate to the influent of wastewater treatment plant was feasible.

Model-Based Evaluation of Hydrothermal Treatment for the Energy Efficient Dewatering and Drying of Sewage Sludge

This research paper evaluates hydrothermal carbonization (HTC) as a possible treatment for sewage sludge, including phosphorus recycling. German governmental requirements force a high number of wastewater treatment plants (WWTP) to recover phosphorus from sewage sludge above limits of 20 g kgTS−1 before further disposal (e.g., co-incineration). The results show that pH reduction has a positive effect on shifting phosphorus to the liquid phase during HTC. Although the experimental results of this research do not yet achieve the necessary phosphorus reduction, various calculations are made to achieve this goal in future experimental studies. In order to be able to assess the energy benefits of HTC, Aspen Plus modeling was used to show the positive impact of implementing this technology in a WWTP. It is shown that the mechanical dewaterability of sewage sludge (SS) increases after HTC enabling energy savings by means of subsequent thermal drying. A heat optimized HTC is able to cut energy expenses by half, further providing a phosphorus-depleted hydrochar for extensive energetic use.

Chemical speciation and risk assessment of heavy metals in biochars derived from sewage sludge and anaerobically digested sludge.

Dewatered sewage sludge (DSS) and anaerobically digested sludge (ADS) were pyrolyzed at 550 °C to investigate the characteristics of derived biochar and evaluate the risk of heavy metals (Cr, Ni, Cu, As, Cd, and Pb). The results showed that the pH value of the biochar derived from DSS (DSS-C) was slightly lower than that of the biochar derived from ADS (ADS-C), while DSS-C presented relatively higher specific surface area and total pore volume. DSS-C also showed higher H/C and lower O/C ratios than ADS-C, indicating a higher aromatic condensation and a lower polarity. Total concentrations of Cr, Ni, Cu, As, Cd, and Pb in DSS and ADS increased significantly after pyrolysis owing to the thermal decomposition of organic matter in the sludge, with corresponding rise of the Nemerow pollution index (NPI) of the biochars compared with the raw sludge. In addition, the sequential extraction procedure (BCR) analysis revealed that the pyrolysis process promoted the transformation of heavy metals from bio-available fractions to stable fractions. The potential environmental risk of heavy metals decreased from moderate and extremely high levels in the DSS and ADS to low risk and moderate levels in DSS-C and ADS-C after pyrolysis, respectively.

Influence of AlCl3 and oxidant catalysts on hydrogen production from the supercritical water gasification of dewatered sewage sludge and model compounds

Hydrogen has attracted significant attention as a clean energy source. Supercritical water gasification (SCWG) technology can produce hydrogen-rich gas while also disposing of sludge. The hydrogen yield from the SCWG of sludge is greatly increased when catalyzed by AlCl3. In this paper, a combined catalyst based on AlCl3 was proposed to further increase the hydrogen yield of SCWG of dewatered sewage sludge (DSS). Analysis of the products from catalytic gasified of DSS and its model compounds were used to propose a catalytic mechanism and reaction pathway of the catalytic SCWG of DSS. Among the combined catalysts used for the SCWG of DSS, 10 wt% AlCl3–H2O2 (mass ratio 8:2) had the best hydrogen production effect, and the hydrogen yield reached 8.88 mol/kg organic matter. This was 14% higher than when catalyzed by 10 wt% AlCl3. During catalysis with AlCl3, Al3+ reacted with OH− in water and precipitated as Al(OH)3, which produced an acidic environment in the liquid product. Al(OH)3 dehydrated to form an AlO(OH) and deposited in the solid product. A small amount of H2O2 promoted the steam reforming reaction of organic matter in DSS, which increased the hydrogen yield. H2O2 further promoted the hydrogen yield in an acidic environment. The catalytic effect of AlCl3 was unaffected by H2O2. The H+ generated by AlCl3 during catalysis promoted H2O2 to further depolymerized organic matter (such as humic substances) in DSS, so that AlCl3–H2O2 catalyzed the SCWG of DSS to further increase the hydrogen yield. The order of hydrogen yield catalyzed by AlCl3–H2O2 was guaiacol > humic acid > glycerol > alanine > glucose. Compared with AlCl3, AlCl3–H2O2 reduced the hydrogen yield of glucose by nearly 20% and increased the hydrogen yield of humic acid by about 17% (25.81 mol/kg feed).

Bioaugmentation mitigates ammonia and hydrogen sulfide emissions during the mixture compost of dewatered sewage sludge and reed straw.

This study investigated the effectiveness of bio-augmenting aerobic cell culture to mitigate ammonia and hydrogen sulfide emission in sewage sludge composting amended with reed straw (with the weight ratio of 1:0.3-0.4). During the 20-day aerated lab-scale composting, adding 200-mL culture (56.80 NTU) reduced ammonia and hydrogen sulfide emissions by 38.00% and 54.32%, and conserved total nitrogen and sulfate by 39.42% and 70.75%, respectively. Organic matters degradation was quick started 1 day ahead. Comparing to the control, nitrate content increased 38.75% at the end of the compost. Bioaugmentation evened the distributions of bacterial communities in the thermophilic phase. The shift was mainly due to 22.97% of relative abundance of Proteobacteria depressed and 157.16% of Bacteroidetes increased, which were beneficial for nitrogen conservation and glycan breakdown, respectively. In summary, the results demonstrated that bioaugmentation addition could be an effective strategy for enhanced sludge composting.

Novel recycling of phosphorus-recovered incinerated sewage sludge ash residues by co-pyrolysis with lignin for reductive/sorptive removal of hexavalent chromium from aqueous solutions

Incinerated sewage sludge ash (ISSA), a by-product generated from the combustion of dewatered sewage sludge, has been extensively studied as a secondary resource for phosphorus recovery by acid extraction methods. Recycling of the P-recovered ISSA residues is crucial to complete and sustain the whole process. In this study, the ISSA residue rich in iron was reused and co-pyrolyzed with lignin at 650, 850 and 1050 °C under N2 atmosphere for the synthesis of a composite material to remove hexavalent chromium (Cr(VI)) from aqueous solutions. Characterization analysis including XRD, XPS, and FTIR showed that iron oxides in the residue were reduced to zero valent iron at 1050 °C that exhibits the optimal Cr(VI) removal performance. The Cr(VI) removal process was rapid and reached a plateau at around 30 min. The maximum removal rate was obtained at pH 2.0, which was conducive for the treatment of a synthetic Cr(VI)-containing wastewater in fix-bed column experiments, whereby Cr(VI) as well as total Cr were continuously removed. Overall, this study proposed a new routine for the recycling of ISSA residue after phosphorus recovery by the acid extraction method and provided a value-added product for Cr(VI) removal from wastewaters.