Bioenergy Recovery Research Articles

Performance of Anaerobic Co-digestion of Pig Slurry with Pineapple (Ananas comosus) Bio-waste Residues

Agro-food industries produce large amounts of bio-waste, challenging innovative valorisation strategies in the framework of circular economy principles. Anaerobic digestion technology is an interesting route to stabilise organic matter and produce biogas as a renewable energy source. This paper aimed to study the optimal performance conditions for anaerobic co-digestion (AcoD) of pig slurry with pineapple (Ananas comosus) peel bio-waste. The anaerobic digestion (AD) trials were performed at lab scale, in a continuous stirred reactor, for 16 days’ hydraulic retention time in mesophilic conditions (37 ± 1 °C). Three hydraulic retention time were performed, one for the reference scenario (T0) and two for AcoD trials (T1, T2). Feeding mixtures (20:80; v:v) of pineapple peel liquor and pig slurry, with an OLR of 1.46 ± 0.04 g TVS L−1reactor day−1 were used during AD/AcoD trials, presenting high values for soluble chemical oxygen demand and C/N ratio. This operational conditions highlight bioenergy recovery up to 0.58 L CH4 g TVSadded−1, in comparison with that obtained with pig slurry substrate (0.31 L CH4 g VSadded−1). The AD performance showed a total volatile solids and chemical oxygen demand removal efficiency of 23% to 47% and 26% to 48%, comparing T0 with the average of T1 and T2, respectively. The digester stability, evaluated by specific energetic loading rate, was below the limit (0.4 day−1) throughout the trials. Pig slurry co-digestion with pineapple peel liquor seems to be a promising approach for potential bioenergy recovery.

Full-scale investigation of ferrous dosing in sewers and a wastewater treatment plant for multiple benefits

This study demonstrates the full scale application of iron dosing in a metropolitan wastewater treatment plant (WWTP) and the upstream sewer system for multiple benefits. Two different dosing locations, i.e., the WWTP inlet works (Trial-1) and upstream sewer network (Trial-2) were tested in this study. Both dosing trials achieved multiple benefits such as sulfide control, phosphate removal and improved sludge dewaterability. During Trial-1, a sulfide reduction of >90% was achieved at high dosing rates (>19 kgFe ML−1) of ferrous chloride in the inlet works and in Trial-2 the in-sewer ferrous dosing had significant gas phase hydrogen sulfide (H2S) concentration reduction in the sewer network. The ferrous dosing enhanced the phosphate removal in the bioreactor up to 76% and 53 ± 2% during Trial-1 & 2, respectively. The iron ending up in the anaerobic sludge digester reduced the biogas H2S concentration by up to 36% and 45%, respectively. The dewaterability of the digested sludge was improved, with relative increases of 9.7% and 9.8%, respectively. The presence of primary clarifier showed limited impact on the downstream availability of iron for achieving the afore-mentioned multiple benefits. The iron dosing enhanced the total chemical oxygen demand removal in the primary clarifier reaching up to 49% at the high dose rates during Trial-1 and 42 ± 1% during Trial-2. This study demonstrated that multiple benefits could be achieved independent of the iron dosing location (i.e., at the WWTP inlet or in the network). Further, iron dosing at both locations enhances primary settling, beneficial for bioenergy recovery from wastewater.

Mechanisms of biohydrogen recovery enhancement from peanut shell by C. guangxiense: Temperature pretreatment ranges from −80 to 100 °C

The potential of low-cost bioenergy recovery from peanut shell was limited for its complex cellulose structure. In order to enhance the total reducing sugar (TRS) yield for bio-H2 production, peanut shell with heat (HT, 50–100 °C) or freezing pretreatment (FT, −80 to 0 °C) under different duration (0.5–12 h) was investigated. For uncovering the enhancement mechanisms, morphological feature and crystalline structure were analyzed by scanning electron microscope (SEM) and X-ray powder diffraction (XRD). The optimal pretreatment of 50 °C for 12 h was obtained with TRS yield increased 73.6%, while the H2 yield of 1.25 ml/mg-TRS was peaked with pretreatment at −80 °C. The SEM and XRD further demonstrated that mechanisms of HT and FT were realized through different ways, which were cracking and collapsing in HT, and delamination and peeling in FT, respectively.

Novel two-chamber tubular microbial desalination cell for bioelectricity production, wastewater treatment and desalination with a focus on self-generated pH control

Microbial desalination cell (MDC) is a new ecofriendly technology that desalinates sea or brackish water by utilizing the electrical energy produced from the oxidation of organics in wastewater. However, pH imbalance as a result of proton accumulation in the anolyte and proton consumption in the catholyte significantly reduces its performance. This research demonstrated, for the first time, the proof-of-concept for a two-chamber tubular MDC (TTMDC) with a new arrangement of the anion and cation exchange membranes. The novel design was aimed to (i) mitigate the pH imbalance through a self-generated pH control mechanism, (ii) reduce internal resistance, and (iii) enhance the recovery of bioenergy in MDC using real seawater as desalination liquid. The results showed that the pH was promisingly balanced using a non-buffered domestic wastewater as the electrolyte with a significant high energy production (8 mW), current generation (43 mA), coulombic efficiency (84%), COD removal (85%) and low internal resistance (10.5 Ω) with 24.3 mg/h of desalination rate in batch operation. The study demonstrated a very promising design of MDC to achieve both the goals of high energy recovery and salt removal with self-generated pH control.

Effect of nitrite addition on the two-phase anaerobic digestion of waste activated sludge: Optimization of the acidogenic phase and influence mechanisms

To simultaneously achieve biological denitrification and bio-energy recovery from sludge, the effects of nitrite on the two-phase anaerobic digestion (AD) of waste activated sludge were explored. Herein, effects of nitrite on the acidogenic phase are optimized, and the corresponding influence mechanisms are investigated. The experimental results show that the optimal nitrite treatment conditions for improving the acidogenic phase are an initial pH of 8.0, a nitrite addition concentration of 500 mg NO2−-N·L−1, and a fermentation time of six days. By comparing the effects of nitrite and nitrate on the acidogenic phase, it was found that it was the nitrite, not the nitrate, that significantly enhanced the sludge organic solubilization, hydrolysis, and acidification, which are primarily attributed to the redox property of nitrite. Based on an analysis of different forms of soluble nitrogen concentrations, there was no obvious accumulation of nitrite or nitrate during the acidogenic phase. An analysis of the methane production and the volatile solid (VS) degradation during the two-phase AD revealed that the nitrite improved the methane production from the methanogenic phase and enhanced the VS degradation of sludge during the entire two-phase AD process. These findings could provide references for simultaneously treating nitrite-rich wastewater and improving anaerobic sludge digestion via two-phase system.

Pyrolysing Horse Manure via Microwave-Induced Heating for Bioenergy Recovery

Transforming waste to energy is essential in view of the need to search for greener and more sustainable energy sources. Such transformation of energy is also aligned with the aim of reducing excessive waste generation whilst creating potential biofuel pathways for power generation. In the present study, animal waste in the form of horse manure is being used as feedstock to undergo microwave-induced pyrolysis via a fixed-bed pyrolysis rig. The relationship of the pyrolysis parameters such as pyrolysis temperature of 350 and 550 ?C, carrier gas flow rate of 0.5 and 1.5 L/min and ratio of horse manure to activated carbon blend of 1:2 and 1:1, with the yield of pyrolysed products is studied. The derived pyrolysis products in the form of solid, liquid and gaseous are characterised and quantified. Result shows that the highest yield of solid, liquid and gaseous products obtained are 78.8 wt%, 24.7 wt% and 34.2 wt%. Solid yield is observed to decrease with increasing pyrolysis temperature while gaseous yield shows a reverse trend. Higher carrier gas flow rate is observed to lower the generation of gaseous and liquid yield while increasing the solid yield. Higher amount of activated carbon within the feedstock is seen to lower the solid yield but increase the gaseous and liquid yields. The liquid yield is found to contain 55.78 wt% of phenolic compounds while gaseous product consists of up to 55 vol% of syngas. The control of the operating conditions in pyrolysis rig enables the production of pyrolysis end products in different phases, generating useful bioenergy and biofertilizer products in the context of circular economy.

High-Rate Anaerobic Digestion of Waste Activated Sludge by Integration of Electro-Fenton Process.

Anaerobic digestion (AD), being the most effective treatment method of waste activated sludge (WAS), allows for safe disposal. The present study deals with the electro-Fenton (EF) pretreatment for enhancing the WAS biogas potential with low-cost iron electrodes. The effect of pretreatment on the physicochemical characteristics of sludge was assessed. Following EF pretreatment, the pH, conductivity, soluble chemical oxygen demand (SCOD), and volatile fatty acids (VFA) increased to 7.5, 13.72 mS/cm, 4.1 g/L, and 925 mg/L, respectively. Capillary suction time (CST) analysis highlighted the dewaterability effect of EF on WAS, as demonstrated by the decrease in CST from 429 to 180 s following 30 min of pretreatment. Batch digestion assays presented an increase in the biogas yield to 0.135 L/g volatile solids (VS) after 60 min of EF pretreatment in comparison to raw sludge (0.08 L/g VS). Production of biogas was also found to improve during semi-continuous fermentation of EF-pretreated sludge conducted in a lab-scale reactor. In comparison to raw sludge, EF-pretreated sludge produced the highest biogas yield (0.81 L biogas/g VS) with a high COD removal rate, reaching 96.6% at an organic loading rate (OLR) of 2.5 g VS/L. d. Results revealed that the EF process could be an effective WAS disintegration method with maximum recovery of bioenergy during AD.

Development of an integrated anaerobic/aerobic bioreactor for biodegradation of recalcitrant azo dye and bioenergy recovery: HRT effects and functional resilience

The efficacy of combined continuous anaerobic-aerobic systems to treat 2-Naphthol Red dye-containing industrial wastewater was investigated. A laboratory-scale of upflow anaerobic sludge bed (UASB) followed by an aerobic process was conducted at a hydraulic residence time (HRT) of 24, 12, 6, and 3 h. The integrated systems showed high performance on the COD removal and decolorization under an HRT of 6 h. The maximum chemical oxygen demand (COD) degradation reached 85.6% and 92.4% in the UASB and the aerobic reactor at organic loading rates (OLR) of 12.97 g COD L−1 d−1, respectively with 98.4% colour removal. At 3 h HRT, the performance of the UASB reactor was deteriorated sharply, however it showed high resistance and rapidly full functions were recovered after stress removal. The maximum methane yield reached 13.3 mmol CH4 g COD−1 d−1 at HRT 6 h and the proposed systems and operating conditions could be extended to full-scale applications.

Positive effects of concomitant heavy metals and their reduzates on hexavalent chromium removal in microbial fuel cells.

Cr(vi) laden wastewaters generally comprise a range of multiple heavy metals such as Au(iii) and Cu(ii) with great toxicity. In the present study, cooperative cathode modification by biogenic Au nanoparticles (BioAu) reduced from aqueous Au(iii) and in situ Cu(ii) co-reduction were investigated for the first time to enhance Cr(vi) removal in microbial fuel cells (MFCs). With the co-existence of Cu(ii) in the catholyte, the MFC with carbon cloth modified with nanocomposites of multi-walled carbon nanotubes blended with BioAu (BioAu/MWCNT) obtained the highest Cr(vi) removal rate (4.07 ± 0.01 mg L−1 h−1) and power density (309.34 ± 17.65 mW m−2), which were 2.73 and 3.30 times as high as those for the control, respectively. The enhancements were caused by BioAu/MWCNT composites and deposited reduzates of Cu(ii) on the cathode surface, which increased the adsorption capacity, electronic conductivity and electrocatalytic activity of the cathode. This study provides an alternative approach for efficiently remediating co-contamination of multiple heavy metals and simultaneous bioenergy recovery.

ASPEN Plus predictive simulation of soft and hard wood pyrolysis for bio-energy recovery

ASPEN Plus predictive simulation of soft and hard wood pyrolysis for bio-energy recovery

ASPEN Plus predictive simulation of soft and hard wood pyrolysis for bio-energy recovery

Thermochemical process such as pyrolysis is one of the most developed options for energy recovery from lignocellulosic biomass sources. A steady-state simulation model was developed for the energy recovery from biomass via pyrolysis using ASPEN Plus v8.8. The biomass feedstocks were beech, Ailanthus and spruce wood. Beech is a hardwood, Ailanthus is a soft hardwood and spruce is softwood. The pyrolysis reactor was modelled by a combination of the yield-shift reactor and the Gibbs reactor. The product yield and composition was calculated by the software via the minimisation of Gibbs free energy method. The simulation was run at atmospheric pressure and 500°C temperature. A bio-oil yield of 62.8% for beech wood, 58.3% for Ailanthus and 54.2% for spruce wood was obtained. Model yield and product composition was validated and considered adequate. The simulation model can be considered as truly predictive for the pyrolysis of soft and hardwood samples in the domain of product yield and product composition.

Kinetic study and performance evaluation of an integrated two-phase fixed-film baffled bioreactor for bioenergy recovery from wastewater and bio-wasted sludge

The present study evaluated the performance of an integrated two-phase fixed-film baffled bioreactor for wastewater treatment with regard to its energy consumption and production. The total potential of the bioenergy recovery of the bioreactor was evaluated not only from the anaerobic wastewater treatment but also from the produced bio-wasted sludge of both phases. Statistical correlations between bio-methane production and kinetic coefficients were uncovered. Methane yields between 0.15 and 0.30 L CH4.g sCODremoved−1 were obtained during anaerobic wastewater treatment. The maximum energy recoveries from the digestion of bio-wasted sludge (sloughed biofilm) equaled 0.28 and 0.3 L CH4. g TS−1 for aerobic and anaerobic units, respectively. The Grau model was appropriate for predicting the performance of the bioreactor and the potential of bio-methane production. It was demonstrated that substrate utilization rate (Rsu) and Grau coefficient (KG) can be applied to predict the rate of methane production. Regarding the volume of treated wastewater, the energy production was in the range of 2.8–12 kWh.m−3. Moreover, the overall energy consumption of wastewater treatment was in the range of 0.32–0.79 kWh/kg sCODremoved, while the total energy production was 3.7–5.1 kWh/kg sCODremoved. Therefore, the designed bioreactor was energy positive with net energy production of 3.39–4.5 kWh/kg sCODremoved−1. The total energy requirement for both wastewater treatment and bio-wasted sludge digestion was 7–15.5% of the total energy production, and, therefore, the bioreactor is a sustainable energy process. The contribution of anaerobic wastewater treatment and anaerobic digestion of bio-wasted sludge of aerobic and anaerobic units for energy recovery as bio-methane was 53, 26, and 21%, respectively. As the bioreactor achieved more than 95% of sCOD removal and have a high bioenergy production, and since kinetic coefficients demonstrated the considerably high performance of the bioreactor, it can be of interest as an appropriate treatment process.

Mechanistic evaluation of the exoelectrogenic activity of Rhodopseudomonas palustris under different nitrogen regimes

The operation of bioelectrochemical systems (BESs) relies on the ability of microbes to export electrons outside of their cells. However, microorganisms are not evolutionary conceived to power BESs as most of the redox processes occur within. In this study, a low cost strategy equivalent to the one used to improve hydrogen production is employed to divert electrons from the metabolism to an electrode. Varying the ratio of nitrogen to carbon concentration (0, 0.20 and 0.54) determines what fraction of the electron flux is directed towards biosynthesis, biohydrogen generation and extracellular electron transfer. The ratio of 0.54 produced a higher specific growth rate while the ratio of 0.20 resulted in combined higher maximum specific hydrogen production and exoelectrogenic activity, translating into a maximum power density of 2.39 ± 0.13 mW m−2 in a novel hybrid hydrogen-photosynthetic microbial fuel cell. The current work sets a framework for the optimisation of R. palustris for bioenergy recovery.

Pretreatment and co-digestion of microalgae, sludge and fat oil and grease (FOG) from microalgae-based wastewater treatment plants

The aim of this study was to assess the co-digestion of residual biomass flows generated in microalgae-based wastewater treatment plants: microalgae, primary sludge and fat, oil and grease (FOG), with and without microalgae thermal pretreatment. The results evidenced the high methane yield of FOG (563 mL CH4/g VS) as compared to microalgae (140 mL CH4/gVS) and sludge (299 mL CH4/g VS). The methane yield of microalgae and sludge co-digestion (50–50% VS) was increased by 25 and 42% by adding 10 and 20% VS of FOG, respectively. Moreover, co-digestion trials improved the anaerobic digestion first-order kinetics by up to 67%. Regarding the thermal pretreatment, it increased the methane yield of microalgae by 60%, and 15% upon co-digestion with sludge and FOG. Therefore, co-digestion of microalgae, primary sludge and FOG appears as a promising strategy to enhance the biogas production, hence bioenergy recovery from wastewater, even without pretreatment.

Effect of Substrate to Inoculum Ratio on Bioenergy Recovery from Food Waste, Yard Waste, and Biosolids by High Solids Anaerobic Digestion

Residual biosolids from wastewater treatment facilities and the organic fraction of municipal solid waste (OFMSW), such as food and yard wastes (FW and YW), are difficult to manage due to increased...

Integrated dark-photo fermentative hydrogen production from synthetic gelatinaceous wastewater via cost-effective hybrid reactor at ambient temperature

The industrial application of anaerobic digestion to treat protein-rich wastewater (e.g., gelatin) is promising; however, inhibitory effects such as released excess ammonia on methanogens causes limitations. This study investigated the potential of sequential dark and photo-fermentation for wastewater treatment and simultaneous bio-hydrogen production (as energy source). To this end, a new configuration, namely dark-photo circular baffled reactor (DP-CBR) was introduced and operated at ambient temperature (21 ± 10 °C). The reactor was composed of four identical compartments, where fluorescent tubes were installed to the last two compartments, i.e., C1-C2 (dark) and C3-C4 (photo). The long-term impact of main operational parameters (i.e., hydraulic retention time [HRT] of 6, 12 and 24 h at initial pH of 5.5 and 6.5) was assessed. Maximum hydrogen yield (HY) of 0.4 L/gCOD, COD removal of 82%, and organic-N removal of 95% were obtained at HRT of 24 h and initial pH of 6.5. Increasing HRT was found to maintain the reactor efficiency at ambient temperature. Lowering initial pH to 5.5 deteriorated the dark-treatment at C1 and C2, resulting in lower local HY and ammonification efficiency. Further, the results confirmed that higher HY was achieved in the photo-fermentation, as the protein hydrolysis was mainly achieved in the dark-fermentation. The residual free ammonia (<0.36 mg/L), at all examined conditions, was below the inhibition limit of photosynthetic bacteria. The microbial community analysis revealed the development of purple non-sulfur bacterial family Rhodospirillaceae at C3. The economic efficiency of DP-CBR was also evaluated by considering the capital cost, annual costs (i.e., lightning, pumping, nutrients, and gas purification), and revenues (i.e., bio-hydrogen energy and removal add-value). Overall, the techno-economic assessment of DP-CBR performance emphasizes its feasibility in affordable removal of organics and bioenergy recovery when dealing with gelatin-rich wastewater.

Predicting heating value of lignocellulosic biomass based on elemental analysis

Heating value is one of the most important properties for bioenergy recovery from lignocellulosic biomass. Various correlations have been established to predict the heating value. This study presents a new correlation to predict the higher heating value (HHV) of lignocellulosic biomass based on its elemental composition: HHV = 0.3443C + 1.192H-0.113O–0.024 N + 0.093S. Compared with the correlations reported in the literature, the relative error of the correlation proposed in this study is lowest, and its coefficient of determination (R2) is highest. Therefore, the new correlation should be capable of providing more accurate HHV prediction than other correlations. For most of the lignocellulosic biomass feedstocks, the absolute percentage errors between the measured HHV and those predicted by using the correlation can be less than approximately 3%. The HHV prediction by using the correlation is satisfactory not only for lignocellulosic biomass feedstocks but also for biochar and various kinds of fossil fuels. Besides, the correlation can be also used for predicting the HHV of other organic matters such as municipal solid waste, industrial waste, and sewage sludge, after the modification of the coefficient before oxygen content based on the characteristics of the matter.

Optimization of Temperature and Inoculum Size for Phycoremediation of Paddy-Soaked Rice Mill Wastewater

AbstractPhycoremediation encompasses microalgae as a sustainable treatment system by integrating the wastewater treatment with bioenergy recovery. However, transforming this technology to real time...

A comprehensive review on toxic petrochemical wastewater pretreatment and advanced treatment

Abstract Petrochemical wastewater is a major industrial source of pollution that produces a variety of refractory and toxic organic pollutants that are detrimental to animals and plants in natural water bodies; it is especially harmful to biological treatment systems. Regardless of these threats, studies on these specific organic pollutants are limited at present. Consequently, it is extremely essential to promote relevant problem solving efficiently. Currently, only limited processes are available for pretreatment of high-concentration wastewater, and advanced treatment of secondary effluent as compared to the conventional treatment are introduced by current studies. Therefore, in this review, we have systematically generalized the characteristics of petrochemical wastewater; we have particularly summarized and compared different methods (recent developments, influencing factors, etc.) which are applied in pretreatment and advancement of current methods. Additionally, the interaction mechanisms of microbes under a wide range of concentrations of specific organic pollutants and associated degradation pathways have been described comprehensively. Moreover, we have analyzed bioenergy recovery from the degradation/removal of specific organic pollutants with environmental-friendly and economically methods because it can help realize the goal of circular resource utilization during the process of detoxification and minimization.

Evaluation of sludge liquors from acidogenic fermentation and thermal hydrolysis process as feedstock for microbial electrolysis cells

In this study, mesophilic acidogenic fermentation, thermophilic acidogenic fermentation, and thermal hydrolysis process (THP) were compared to generate sludge liquors for bioenergy recovery with microbial electrolysis cells (MECs). The results showed that THP at 170 °C was the most effective for hydrolysis of particulate organics in sewage sludge, while fermentation under thermophilic temperature led to the highest accumulation of volatile fatty acids (VFAs) in sludge liquor. However, THP yielded the highest percentage of acetate in VFAs, which resulted in superior MEC performance compared to fermented sludge liquors in terms of current density (2.7 vs. ~1.3 A/m2), coulombic efficiency (50% vs. 31–34%), bio-H2 potential (1114 vs. 839–881 mL), and H2 production rate (50.3 mL/d vs. 28–32 mL/d). The utilization sequence of the VFAs was found to be acetate > butyrate > propionate. Overall, our results show that generating sludge liquors through THP could provide a feasible solution to produce bio-H2 from sewage sludge; however, coulombic efficiencies should be further improved before practical application.