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Anaerobic digestion (AD) is a prominent treatment method for the sludge produced from sewage treatment plants. Poor solid reduction and longer retention time are the main drawbacks of AD. Thermal hydrolysis (TH) is a potential pretreatment method for solubilization of sewage sludge (SS) solids thereby improving biogas production during AD post-treatment. In this study, the SS sample (total solids = 1.75 wt% and total chemical oxygen demand (COD) = 15,450 mg L−1) was subjected to TH pretreatment (temperature = 140–180°C and reaction time = 60 minutes) in a 0.7-L capacity stainless-steel high-pressure reactor. At a reaction temperature of 180°C, the maximum solid solubilization (total dissolved solids = 4652 mg L−1) and improved dewaterability (time to filter = 4.7 s.L g−1) were observed. The biochemical methane potential test results showed almost doubling of methane generation from 145 to 284 mL gCOD−1 after TH pretreatment at 180°C. The life cycle assessment approach was used to compare various SS treatment and disposal scenarios, two of which included hydrothermal pretreatment. The scenarios involving hydrothermal pretreatments showed the least global warming potential. [ABSTRACT FROM AUTHOR]

Waste disposal is a challenging environmental concern worldwide. Carbon-rich waste materials can be transformed into adsorbent and/or catalyst support to reduce treatment costs and promote waste recycling. In the present study, three waste materials—sewage sludge, black liquor (from pulp and paper mills), and sugar mill press mud—were converted into activated carbons which were used as support for the iron-impregnated heterogeneous Fenton-type photo catalysts. These materials were characterized and tested on synthetic wastewater containing 4-chlorophenol (4-CP) as the model compound and simulated pulp-bleaching effluent. The oxidation runs were performed at an initial reaction pH of 4.4 with stoichiometric H2O2 dose and catalyst mass loading of 1 g/L for 2 h duration. The maximum total organic carbon removal of 69% and 32% was observed for 4-CP and simulated bleaching effluent, respectively, during photocatalytic oxidation with black liquor–derived catalyst. Thus, the use of black liquor–derived catalyst for bleaching effluent can help paper mill operators handle liquid as well as solid waste in a very efficient manner. [ABSTRACT FROM AUTHOR]

• HTC pretreatment greatly improved resource recovery from sewage sludge. • The properties of hydrochar formed after HTC at 200 °C resembled with peat coal. • TGA kinetics of hydrochar combustion showed great reduction in activation energy. • 60–70% HA and 80% PO 4 3−-P (struvite) were recovered from process wastewater. • The recovered HA showed improvement in seed growth. Safe disposal of the sludge generated from sewage treatment plant is a major challenge worldwide. Hydrothermal carbonization (HTC) is considered a potential pretreatment alternative for sewage sludge to facilitate the improved resource recovery. In the present study, the mixed centrifuged sewage sludge (CSS) was subjected to the HTC pretreatment to determine characteristics of the solid hydrochar (HC) and liquid fraction (LF) with a purpose of energy recovery and extraction of value-added compounds, respectively. HTC was performed in a high pressure batch reactor at 200 °C temperature for 1–8 h duration. The HC produced after HTC resembled with the low quality peat coal whereas the LF contained value-added chemicals such as humic acid (HA) and phosphate phosphorous (PO 4 3—P). Using ammonium sulphate as 'salting out' agent, ~70% of the total HA (~15–16 g/L) could be recovered from the LF. Using the recovered HA, an improvement in the root and shoot lengths of the seeds could be observed. In the subsequent step, the total PO 4 3−-P recovery of ~80% was obtained as struvite from the residual wastewater. [ABSTRACT FROM AUTHOR]

Abstract Land disposal of waste activated sludge pose environmental risks due to the presence of heavy metals, pathogens and organic pollutants. Anaerobic digestion (AD) is one of the preferred treatment methods for sludge treatment. However, sludge hydrolysis is often found the rate-limiting step thereby reducing the biogas generation potential. Therefore, an effort was made to determine the optimum conditions for sludge solubilization by means of hydrothermal pretreatment. In this study, response surface methodology using Box Behnken design approach was used to optimize four hydrothermal reaction variables (i.e., initial pH, time, temperature, and oxidation coefficient) for sludge solubilization and total chemical oxygen demand (tCOD) reduction. Temperature and pH were found to be the most significant parameters. The maximum tCOD reduction and volatile suspended solids solubilization of 58% and 52%, respectively, were obtained at the following optimum conditions: temperature = 180 °C, time = 5 h, pH = 3.3 and oxidation coefficient = 0.5. Under similar conditions and alkaline pH, Maillard's reaction occurs which may have adverse impact on the performance of downstream AD process. The highest NH 4 + N and volatile fatty acids (VFAs) concentrations were detected in the treated sludge at the optimum conditions. The future studies should be aimed at the recovery of proteins, VFAs and biogas using appropriate methods. Graphical abstract Image 1 Highlights • Box Behnken design approach was used to optimize conditions for WO and TH. • TH treatment of sludge in acidic pH range eliminates the Maillard's compounds. • Alkaline conditions resulted in poor dewatering of treated sludge. • WO causes the degradation of molecules to form volatile fatty acids. • Hydrothermal pretreatment can improve resource recovery from sewage sludge. [ABSTRACT FROM AUTHOR]

Scientific disposal of sewage sludge (SS) is a tedious task worldwide. Landfilling of the SS after centrifugation may have serious adverse impacts on the environment. The present study investigated efficacy of hydrothermal carbonization (HTC) as pretreatment for the centrifuged sewage sludge with an aim to improve resource recovery. In this study, both solid and liquid fractions recovered after the HTC were subjected to the detailed analysis for examining the opportunities for recovery of value-added chemicals and biogas. The HTC conditions were optimized using design of experiments (DOE) approach. The runs were performed in a high-pressure reactor at 160–240 °C temperatures and total pressures of 6.1–34.2 kg/cm2 for 1–3 h duration without supply of air. The optimum HTC temperature and duration were found to be 200 °C and 1 h, respectively. Under these conditions, the dried hydrochar (HC) had higher heating value of ~13 MJ/kg. Its properties were found similar to that of the sub-bituminous coal based on the atomic ratio of elements. The HTC pretreatment resulted in substantial reduction in carbon and oxygen due to decarboxylation, dehydration and oxidation (due to oxygen present in reactor headspace) reactions. The process wastewater (PWW) recovered after HTC at the optimum conditions had high concentration of the recoverable value-added compounds such as humic acid (HA) and PO 4 3--P (concentration = 20 g/l and ~0.5 g/l, respectively). Moreover, significant quantity of biogas could be generated from the PWW. Hence, hydrothermal pretreatment can be considered a potential option for SS valorization. [Display omitted] • HTC of centrifuged SS showed good recovery potential at 200 °C temperature. • Distribution of C and N in solid, liquid and gaseous phase was obtained. • More than 220 ml/g sCOD biogas production was observed from process wastewater. • EEM spectra showed high concentration of HA and FA after HTC at 200 °C temperature. • Using HTC pretreatment, recovery of non-renewable PO 4 3--P may also be possible. [ABSTRACT FROM AUTHOR]

In the present study, the performance of sewage sludge based adsorbents was examined for the removal of two recalcitrant pollutants (i.e. lignin and amoxicillin) from synthetic wastewater solutions (adsorbate concentration = 50–250 mg/l). The effect of various reaction parameters such as wastewater pH, adsorbent dosage and temperature was studied. Possible mechanisms for the adsorption process have been proposed which depends upon the behaviour of adsorbent surface and adsorbate molecules under specific reaction conditions. Three-parameter Redlich–Peterson isotherm model was found the best fit to the equilibrium data. Pseudo first and second order models validated the kinetic data for lignin and amoxicillin adsorption systems, respectively and the corresponding activation energy was 3.5–4.5 and 12–22 kJ/mol. The nature of adsorption was elucidated from the thermodynamic parameters. [ABSTRACT FROM AUTHOR]

The present study deals with the characterization of primary sewage sludge-derived activated carbons which were used for phenol adsorption from the synthetic wastewater. The waste-derived adsorbents were prepared by a two-step process: chemical activation (with ZnCl and KOH) followed by pyrolysis. The mesoporous adsorbents were found to have BET surface area comparable to commercial activated carbon (surface area = 495-515 m/g). The adsorption runs were performed in orbital shaker with synthetic phenolic wastewater (phenol concentration = 50-250 mg/L) to investigate the effect of various reaction parameters. The equilibrium phenol adsorption data could be described by Redlich-Peterson isotherm model and the pseudo first-order kinetic model exhibited the best fit to time-based adsorption data. The phenol adsorption was endothermic for all adsorbents. The performance of the thermally regenerated waste-derived adsorbents in the wastewater treatment was found to reduce significantly. [ABSTRACT FROM AUTHOR]

In the present study, sewage sludge (SS) was used to synthesize activated carbon (AC) which was further utilized as adsorbent for the removal of ciprofloxacin (CPX) from synthetic wastewater. The adsorbent was prepared by chemical activation method using ZnCl2 as activating agent. Design of experiments (DOE) approach was explored to determine the optimum operating conditions for the synthesis of AC and CPX removal from the wastewater. The optimum conditions for AC synthesis (i.e., carbonization temperature = ~500°C, activation time = 30 min, and impregnation ratio = 2.26) were decided based on results for three response parameters, that is, adsorbent yield, methylene blue removal, and iodine number. The synthesized adsorbent showed ~93% CPX removal (initial CPX concentration = 100 mg/L) at the following optimum conditions: adsorbent dose = 1.31 g/L, pH = 7 and reaction time = 12 h. Langmuir isotherm model was best fit to the equilibrium adsorption data (maximum adsorption capacity of SS derived AC = 102 mg/g) whereas pseudo‐second order model showed the best fit to adsorption kinetic data (adsorption capacity = 77.5 mg/g). An effort was also made to reduce fresh water requirement for adsorbent synthesis by recycling the wastewater produced during chemical activation of SS. Practitioner points: Experiment design approach was used for optimization of adsorbent preparation conditions and CPX removal conditions by waste derived adsorbent.Sewage sludge derived adsorbent had BET surface area of 564 m2/g which is comparable to commercial activated carbon.93% CPX adsorption with the sewage sludge derived adsorbent at optimum conditions.Langmuir model better suited the CPX adsorption data.Wastewater recycling and ZnO recovery from wastewater produced during adsorbent synthesis were performed. [ABSTRACT FROM AUTHOR]

In this study, the performance of activated sludge derived granular activated carbon (SGAC) was investigated for ciprofloxacin (CPX) removal from synthetic and simulated wastewaters in a fixed-bed adsorption column operated in continuous mode. The adsorbent was synthesized using chemical activation using ZnCl 2 as activating agent. Its surface area and pore volume were found comparable to that of the commercial granular activated carbon (CGAC). The maximum saturation adsorption capacities for CPX were ~16 mg/g and ~14 mg/g, respectively, with SGAC column under identical operating conditions (CPX concentration = 50 mg/L, bed height = 4 cm and wastewater flow rate = 1.5 mL/min) for synthetic and simulated wastewaters. The presence of other organics reduced CPX adsorption capacity of SGAC. The breakthrough curve data for both wastewaters could be adequately fit in Thomas and Yoon-Nelson kinetic models. The addition of H 2 O 2 in wastewater showed no considerable improvement in CPX removal. However, H 2 O 2 oxidation of spent adsorbent exhibited better results compared to thermal treatment for adsorbent regeneration. The results showed that sewage sludge can be recycled as an efficient adsorbent for the removal of recalcitrant organic pollutants from wastewater. Image 1 • CPX removal by activated sludge derived AC was studied in a fixed bed column. • The effect of particle size and matrix components on CPX removal was investigated. • In comparison to adsorption, Fenton-like oxidation slightly improved CPX removal. • The breakthrough curve data could be adequately fit in Thomas and Yoon-Nelson models. • Peroxide oxidation of waste derived AC was better than thermal regeneration process. [ABSTRACT FROM AUTHOR]