Volatile Solids Removal Research Articles

Advanced anaerobic co-digestion of hydrothermally pretreated wheat straw: Process performance, techno-economic and life cycle assessment.

Hydrothermal and thermal-alkali pretreatment potential was investigated to enhance agro-wastes' anaerobic co-digestion (AcoD). The techno-economic (TEA) and life cycle assessment (LCA) of biogas upgrading (BioCNG) and energy generation via combined heat and power (CHP) processes for energy utilization were carried out to realize the environmental impacts and cost-effectiveness of the studied processes. Three AcoD conditions of untreated, hydrothermally (150°C, 60min) and thermal-alkali pretreated (1% NaOH, 150°C- 60min) wheat straw (WS) with food waste and cow manure were studied in semi-continuous mode for 340 days under variable organic loading rates (OLR, 1.25-3.75 gVS/L.d). At an OLR of 1.67 gVS/L.d and 45 days HRT, the methane yield and volatile solids removal in control digester were 231 mL/gVS and 39.7%, and in thermal-alkali pretreated digester were 302 mL/gVS and 53.3%, presenting an increase of 30% and 34% over control, respectively. The LCA and TEA of all three processes under 45 days of HRT operations were carried out. The environmental performance evaluation across various scenarios indicated that integrating pretreatment with the combined heat and power (CHP) process significantly lowered the global warming potential (GWP), outperforming the BioCNG process. In particular, hydrothermal pretreatment made the largest contribution to the reduction in GWP, achieving a value of -0.1935kg CO2-equivalent, primarily due to energy generation from the CHP process. In comparison, the BioCNG process recorded a GWP of -0.0377kg CO2-equivalent. This result demonstrates that the CHP process led to an 81% greater reduction in GWP than the BioCNG process. While the BioCNG process surpassed CHP in terms of economic performance, the hydrothermal pretreatment scenario proved to be financially the most advantageous, with a net present value (NPV) of $10.16 million, an internal rate of return (IRR) of 13%, and a shorter payback period (PBP) of 14 years.

Potentialities of semi-continuous anaerobic digestion for mitigating antibiotics in sludge.

The behavior and removal of roxithromycin (ROX), oxytetracycline (OTC), chlortetracycline (CTC), and enrofloxacin (ENR) were investigated during the steady state of sludge anaerobic digestion (AD) in semi-continuous mode (37°C). Sludge was spiked at realistic concentrations (50μg/L of each antibiotic) and then used to feed the bioreactor for 80days. Antibiotics were extracted from the substrate and digested sludge samples by accelerated solvent extraction (ASE). Accurate determination of antibiotics was obtained by the standard addition method (SAM) associated with the liquid chromatography-tandem mass spectrometry (LC-MS/MS). The presence of antibiotics at a concentration of 2.5μg/g TS had no inhibitory effects on methane (CH4) production, total and volatile solids (TS and VS) removal as well as chemical oxygen demand (COD) removal. During the steady-state, antibiotics were removed significantly by 50, 100, and 59% respectively for the ROX, OTC, and CTC. Furthermore, ENR removal was not statistically significant and was estimated at 36%. This study highlighted that AD process could partially remove parent compounds, but ROX, CTC, and ENR persisted in the digested sludge. Hence, AD could be considered as a sludge treatment for mitigating, but not suppressing, the release of antibiotics through sludge application.

Bioenergy potential of paper waste: Fungal pretreatment and kinetics modelling

Using the fungi Phanerochaete chrysosporium and Aspergillus niger as a biopretreatment agent to improve degradation of lignocellulosic paper with analogous increase in biogas production, anaerobic digestion (AD) was executed. Milled and hydrothermally-treated (HT) or steamed paper were separately inoculated for 360 hr at 28 °C with each fungal species, with an uninoculated treatment as control. AD experiment was conducted in bench-scale batch bioreactors for 48 days at 40°C. The initial characteristics of the feedstock and inoculum were examined in addition to biomethane yield, total and volatile solids degradation, and lignocellulosic content removal. The pretreatment of milled paper with P. chrysosporium resulted in the highest biogas yield of 1035 mL/gVS, followed by A. niger with a yield of 550 mL/gVS. These values represented a significant increase (p < 0.05) of 226 % and 73 % compared to the untreated feedstock, respectively. P. chrysosporium pretreatment achieved the highest total solids removal of 66.85 %, whereas A. niger pretreatment resulted in the maximum volatile solids removal of 64.63 % in HT-paper waste. P. chrysosporium also exhibited the highest lignin removal efficiency, with 84.31 % in milled feedstock and 79.17 % in the steamed state. A. niger showed 77.28 % and 67.09 % lignin removal in the milled and HT paper, respectively. The study demonstrated that pretreatment with P. chrysosporium and A. niger significantly (p<0.05) improved biogas production by facilitating the biodegradation of lignocellulosic components. All measured biomethane data from experiments fitted adequately to the modified Gompertz model with R2 ranging from 0.97 to 0.99.

Solid-state anaerobic digestion of sweet corn waste: The effect of mixing and recirculation interval

The mixing and sludge recirculation interval is one of the key successes of the solid-state anaerobic digestion process, a promising technology for converting high-solid agro-industrial wastes to renewable energy. This study employed a pilot-scale completely stirred tank reactor to examine biogas production from sweet corn waste, including corn cobs, husks, and seeds. The reactor was operated as solid-state anaerobic digestion at an ambient temperature. The mixing and recirculating intervals were set to non-mixing and mixing for 10 minutes every 3, 6, and 12 hours. The initial total solid of the feedstock was 25%, while the hydraulic retention time was 30 days. The results showed that during the mixing and recirculation every three hours, the highest chemical oxygen demand, total solid, and volatile solid (VS) removal efficiencies were 85.42%, 62.92%, and 64.59%, respectively. The ratio between volatile fatty acid and alkalinity ranged between 0.20 and 0.30 without any sign of system failure. The highest specific methane yield of 766 L/kg VSadded was obtained in the experiment with mixing and recirculating intervals every 3 hours. It was found that the modified Gompertz model could effectively fit the methane yields with an R2 of 0.9667. The modeled methane production potential and the maximum methane production rate were 867.40 NL/kg VSadded and 132.01 NL/kg VSadded-d, respectively. Additionally, the levelized cost of the biogas produced from the solid-state anaerobic digestion of the sweet corn waste was calculated to be 0.61 USD/kg. The findings of this study can serve as a guide for the design and operation of the SS-AD system, which aims to transform various types of lignocellulosic waste into environmentally friendly energy.

Yeast culture enhances long-term fermentation of corn straw by ruminal microbes for volatile fatty acid production: Performance and mechanism

Ruminal microbes can efficiently ferment biomass waste to produce volatile fatty acids (VFAs). However, keeping long-term efficient VFA production efficiency has become a bottleneck. In this study, yeast culture (YC) was used to enhance the VFA production in long-term fermentation. Results showed that YC group improved the volatile solid removal and VFA concentration to 47.8% and 7.82 g/L, respectively, 18.6% and 16.1% higher than the control, mainly enhancing the acetic, propionic, and butyric acid production. YC addition reduced the bacterial diversity, changed the bacterial composition, and improved interactions among bacteria. The regulation mechanism of YC was to increase the abundance and activity of hydrolytic and acidogenic bacteria such as Prevotella and Treponema, improve bacterial interactions, and further promote expression of functional genes. Ultimately, a long-term efficient ruminal fermentation of corn straw into VFAs was achieved.

Optimized thermal pretreatment for lignocellulosic biomass of pigeon pea stalks to augment quality and quantity of biogas production

By applying heat to the feedstock during the thermal treatment of biomass for the production of biogas, the organic material's biodegradability can be greatly increased. Biogas production is a huge research area for alternate energy production technology. Increased biodegradability, improved methane yield, pathogen, and weed seed destruction, and overall process efficiency are all benefits of this type of pretreatment. It is a useful pretreatment technique for maximizing the production of biogas because it can decrease inhibitory compounds, and increase the digestibility of biomass. This work focused on increasing the efficiency of biogas production from lignocellulosic biomass of pigeon pea stalks by a novel thermal pretreatment. The pigeon pea stalk is initially imposed to physical pretreatment (PT) by an automatic hammer mill which is considered as a base for comparing performance. Thermal pretreatment was carried out for one hour, and two hours durations at different temperatures like 100 °C, 125 °C, 150 °C, 175 °C, and 200 °C. Compared to physically pretreated pigeon pea stalks, 200ᴼC thermal pretreated pigeon pea stalks for two hours have produced 88.41 % higher biogas, 16.14 % increase of cellulose, 19.9 % higher volatile solid removal, and 3.94 % lesser lignin. The enhanced chemical characteristics were ensured by analyzing the chemical composition variations through the FTIR, XRD, and SEM images. So, this is recommended for enhanced biogas production.

Production of biogas from various types of spent mushroom substrate under different growth conditions

The mushroom cultivation industry effectively utilizes a diverse range of lignocellulosic waste but generates a significant amount of spent mushroom substrate (SMS) that poses disposal challenges. However, SMS can be used to generate valuable biogas. This study aimed to generate biogas by utilizing different types of spent mushroom substrate (SMS) obtained from three mushroom varieties. These mushroom varieties were cultivated in three types of greenhouses: Photovoltaic Shading greenhouse (PSG), shading greenhouse (SHG), and Control greenhouse (CG). The study found that the total solids (TS) and the amount of SMS used had a significant impact on both the total gas production and the removal of volatile solids (VS). The results demonstrated the feasibility of utilizing SMS as a raw material for biogas production, with variations observed depending on SMS type and greenhouse conditions. It contributes to knowledge in sustainable waste management and renewable energy production from agricultural by-products.

Alkaline hydrothermal cracking effect and substance transformation characteristics of caprolactam-containing sludge

Caprolactam is a crucial chemical intermediate, but its wastewater treatment process generates a significant amount of caprolactam-containing sludge. This study represented the first exploration of the effects of alkaline hydrothermal technology on the cracking and transformation of substances in this sludge. The cracking effect of caprolactam-containing sludge during hydrothermal treatment increased with rising reaction temperature and longer reaction time. With NaOH dosage in hydrothermal treatment increasing from 0 to 2 wt%, the volatile suspended solids (VSS) removal rate of the sludge increased from 44.5% to 74.8%, soluble chemical oxygen demand (SCOD) in the cracking liquid increased from 12772 mg/L to 22976 mg/L, and ammonia nitrogen concentration increased from 398.0 mg/L to 851.2 mg/L. However, the addition of Ca(OH)2 did not significantly affect the changes of sludge suspended solids, VSS and SCOD concentration, but increased the leaching of ammonia nitrogen (up to 745.0 mg/L). This was due to the secondary flocculation of Ca2+, which rebound with dissolved non-proteinaceous organic matter. Increasing temperature, reaction time, and alkaline dosage all enhanced the fluorescence intensity of dissolved organic matter (DOM). Moreover, higher reaction temperature and alkaline dosage reduced the proportion of proteinaceous products in DOM while increasing the proportions of fulvic acids, soluble microbial metabolites, and humic acid-like substances. The study provided crucial theoretical support for engineering application of this technology.

Bioenergy recovery from waste engine oil through anaerobic co-digestion with sewage sludge: Effects of total solids and inoculum to substrate ratio

ABSTRACT Considering their various benefits, such as pollution control, waste management, and eco-friendly energy production, much more attention is currently devoted to utilization of some urban, industrial, and agricultural wastes in the course of anaerobic digestion (AD) across the world. From this perspective, the present study aimed to evaluate prospects of biogas production from waste engine oil (WEO) through its co-digestion (CoD) with activated municipal sewage sludge (SS). In order to do this, AD was carried out in batch-mode 1-L reactors at a mesophilic temperature of 35°C, with consideration for total solids (TS) levels of 3% and 6% and inoculum-to-substrate ratios (ISRs = 0.5, 1, and 2), which were based on volatile solids (VS), over a period of 85 days. The treatment with TS = 6% and ISR = 2, or 6874 mL, showed the maximum biogas generation rate, according to the trials, with TS and VS removal values of 23% and 28%, respectively. As well, reactor monitoring during AD revealed that the parameters of potential of hydrogen (pH) and alkalinity recovered following acidification after 7 days, and the relatively low efficiency of the given process (0.233 m3/kg-VSadded) was attributed to the highly complicated and difficult-to-degrade structure of WEO. The kinetics of anaerobic CoD consistently established that the maximum cumulative biogas production rate (Rm = 5.61 m3/kg-VSadded.d) and the shortest biogas production lag time (λ = 0) occurred when there were TS = 3% and 6%, in that order. Moreover, kinetic models, i.e. the Modified Gompertz and Logistic Function ones, were found to be in very good agreement with experimental data, whereas the first-order model failed to offer ideal predictions of biogas production trend in most cases.

Enhancement of Fermentation Performance in the Anaerobic Co-Digestion of Chicken Manure and Corn Straw under Biogas Slurry Reflux via Air Stripping of the Digestate

Ammonium inhibition is a key limiting factor for anaerobic digestion when using chicken manure as the main substrate, especially in a digestion system with biogas slurry reflux. Air stripping is usually used as a recycled biogas slurry treatment. In this study, we carried out the anaerobic co-digestion of chicken manure and corn straw. The fermentation performance was investigated with and without air stripping at different biogas slurry reflux ratios and with an increasing organic loading rate. The results show that air stripping enhanced biogas production, system stability, and volatile solid removal efficiency via the mitigation control of ammonium inhibition. The total ammonium nitrogen in the digesters with air stripping was 20.24–46.40% lower than in those without air stripping. The highest specific biogas production and volatile solid removal efficiency values were obtained in the digesters at an organic loading rate of 3.3 g volatile solid (VS)/(L·d) and a reflux ratio of 75% with air stripping, reaching 480.43 mL/gVSadd and 63.36%, respectively. Moreover, air stripping also improved the organic loading rate and reflux ratio. Stable operation was achieved at an organic loading rate of 5.3 gVS/(L·d) and a reflux ratio of 75%, with specific biogas production of 392.35 mL/gVSadd and a volatile solid removal efficiency of 50.33%. The fermentation performance deteriorated when the organic loading rate was increased to 8.0 gVS/(L·d) at a reflux ratio of 75%, even when air stripping was conducted, indicating that a slighter lower reflux ratio (50%) could be more feasible at a higher organic loading rate (8.0 gVS/(L·d). Additionally, the methanogen community structure varied according to the use of air stripping, with a shift in the methanogenic pathway from hydrogenotrophic to acetoclastic methanogens. Overall, our findings support the adoption of air stripping for ammonium mitigation in anaerobic digestion with biogas slurry reflux.

Alkaline Pre-Fermentation Promotes Anaerobic Digestion of Enhanced Membrane Coagulation (EMC) Sludge: Performance and Microbial Community Response

Concentrating organic matter in sludge and converting it into methane through anaerobic bioconversion can improve resource recovery from domestic wastewater. Enhanced membrane coagulation (EMC) is highly efficient at concentrating organic matter, but residual coagulants (aluminum salts) can obstruct bioconversion by blocking microbial access. Limited research exists on evaluating EMC sludge bioconversion performance and addressing coagulant inhibition. This study proposes alkaline pre-fermentation to break down HO-Al-P backbones in coagulated sludge flocs, thereby improving hydrolysis and organic acid production for anaerobic digestion. Among the tested alkaline conditions (pH 9, pH 10, pH 11), pre-fermentation at pH 11 released the most organic matter (4710.0 mg/L SCOD), 20.4 times higher than without alkaline treatment. At pH 11, phosphate (61 mg/L PO43−–P) and organic acid production (2728.1 mg COD/L, with nearly 50% acetic acid) peaked, resulting in superior volatile solids removal (65.2%) and methane production (185.8 mL/g VS) during anaerobic digestion. Alkaline pre-fermentation favored alkali-tolerant bacteria such as Firmicutes and Actinobacteria, especially at pH 11, while neutrophilic Proteobacteria were suppressed. Trichococcus and Bifidobacterium, known acid producers, dominated under all conditions, with their abundance increasing at higher pH levels. Anaerobic digestion enriched fermentative bacteria like Chloroflexi and Synergistota (e.g., Thermovirga), especially in high pH reactors. Methanothrix, an acetoclastic methanogen, became the dominant methanogenic archaeon, indicating that methane production from EMC sludge primarily followed the acetoclastic methanogenesis pathway. Our findings demonstrate that alkaline pre-fermentation at pH 11 significantly enhances the hydrolysis efficiency of EMC sludge for methane recovery.

Anaerobic co‑digestion of bovine ruminal waste and brewery spent grain: Effects of inoculum to substrate ratio, mixing ratio, process stability, organic matter removal, and methane yield

The technological potential of co-digesting bovine rumen waste (BRW) with brewery spent grain (BSG) is significant, offering enhanced biogas production and effective waste management. This study's findings demonstrate that the anaerobic digestion process becomes significantly more efficient when difficult to degrade BRW is combined with easily degradable BSG. The highest methane yield obtained in the mono-digestion of BRW was 127.11 NmLCH4 gVS−1 with biodegradability of 33.89 % in inoculum to substrate ratio (ISR) 2, and for de BSG obtained was 304.18 NmLCH4 gVS−1 with biodegradability of 68.26 % in ISR 4. The overall average obtained in co-digestion for volatile solids (VS) removal was 26.28 %, and the concentration of methane present in the biogas was 57.18 %. The VS removal efficiency and the increase in biogas and methane yield were directly proportional to the rise in ISR and the proportion of BSG in the mixture. Specifically, the ideal mix of 25 % BRW with 75 % BSG at ISR 4 resulted in a notable methane yield of 255.30 NmLCH4 gVS−1. This process stabilizes digestion and significantly improves solids removal and methane concentration, making it a highly efficient solution for sustainable energy production and industrial waste management.

Pilot-scale evaluation of cascade anaerobic digestion of mixed municipal wastewater treatment sludges.

This work assessed the performance of a pilot-scale cascade anaerobic digestion (AD) system when treating mixed municipal wastewater treatment sludges. The cascade system was compared with a conventional continuous stirred tank reactor (CSTR) digester (control) in terms of process performance, stability, and digestate quality. The results showed that the cascade system achieved higher volatile solids removal (VSR) efficiencies (28-48%) than that of the reference (25-41%) when operated at the same solids residence time (SRT) in the range of 11-15 days. When the SRT of the cascade system was reduced to 8days the VSR (32-36%) was only slightly less than that of the reference digester that was operated at a 15-day SRT (39-43%). Specific hydrolysis rates in the first stage of the cascade system were 66-152% higher than those of the reference. Additionally, the cascade system exhibited relatively stable effluent concentrations of volatile fatty acids (VFAs: 100-120 mg/l), while the corresponding concentrations in the control effluent demonstrated greater fluctuations (100-160 mg/l). The cascade system's effluent pH and VFA/alkalinity ratios were consistently maintained within the optimal range. During a dynamic test when the feed total solids concentration was doubled, total VFA concentrations (85-120 mg/l) in the cascade system were noticeably less than those (100-170 mg/l) of the control, while the pH and VFA/alkalinity levels remained in a stable range. The cascade system achieved higher total solids (TS) content in the dewatered digestate (19.4-26.8%) than the control (17.4-22.1%), and E. coli log reductions (2.0-4.1 log MPN/g TS) were considerably higher (p < 0.05) than those in the control (1.3-2.9 log MPN/g TS). Overall, operating multiple CSTRs in cascade mode at typical SRTs and mixed sludge ratios enhanced the performance, stability digesters, and digestate quality of AD. PRACTITIONER POINTS: Enhanced digestion of mixed sludge digestion with cascade system. Increased hydrolysis rates in the cascade system compared to a reference CSTR. More stable conditions for methanogen growth at both steady and dynamic states. Improved dewaterability and E. coli reduction of digestate from the cascade system.

Effects of reaction temperature and oxygen pressure on dissolved organic matter in hydrothermal reactions of municipal sludge: A comprehensive analysis

The impact of temperature and oxygen pressure on the basic performance of hydrothermal reactions and dissolved organic matter (DOM) was investigated. The results showed that total chemical oxygen demand and volatile suspended solids removal rate achieved a maximum of 72 % and 99 %, respectively, at 260 °C and 0.9 MPa oxygen pressure. Oxygen demonstrated a significant role in enhancing sludge particle dissolution. The interaction with temperature resulted in a complex trend for dissolved organic carbon (DOC) and specific ultraviolet absorbance at 254 nm. Acetic acid and formic acid were identified as the prominent volatile fatty acids, with formic acid prevalent at lower temperatures, while acetic acid accumulated with increasing temperature and oxygen pressure. Three-dimensional excitation emission matrix and Fourier transform ion cyclotron resonance mass spectrometry was also employed to analyse DOM as over half of the DOC remained unknown. Parallel factor analysis indicated that three components with 8 peaks in total might represent a universal feature for fluorescent DOM in hydrothermal reaction solution. The deciphered data from FTICR-MS indicated that lipids and lignins as well as CHOS and CHON molecules were the main components of DOM. Meanwhile, condensed hydrocarbons were formed at high temperatures in wet oxidation runs. Moreover, identification of C19H32O3S, C18H30O3S and C18H26N2O3 as crucial intermediates further enriched the understanding of hydrothermal reactions in municipal sludge.

Efficient methane production from anaerobic co-digestion of lignin-based feedstock and waste plastic: Digester performance and microbial community structures

Waste plastic (WP) and lignocellulosic biomass (LCB) are both refractory polymers that can provide feedstocks for the production of fuels. Anaerobic digestion (AD) is a widely recognized technology utilized in waste management and renewable energy production. It involves the utilization of microorganisms to decompose organic matter into methane (CH4). Nevertheless, mono-digestion, which refers to AD utilizing a single feedstock, encounters difficulties related to the properties of the feedstock. Therefore, the utilization of co-digestion with multiple feedstocks provides the potential to overcome these limitations. This study might be the first to examine the impact of co-digestion of low-density polyethylene (LDPE) with rice straw (RS) for biogas and CH4 production. The cumulative CH4 production for AD-1, AD-2, AD-3, AD-4, AD-5, and AD-6 was 154.9, 177.4, 52.0, 81.2, 98.43, and 135.15 NmL/g VS. The methane energy yields varied between 2.29 and 7.64 MJ/m3, while their respective βece values spanned from 17.6 to 58.8 %. Volatile solid removal was enhanced for the treated RS-LDPE mixture, as demonstrated in AD-6, in comparison to the untreated substrate in the AD-2 digester. There is a notable disparity in the composition of bacterial communities within the bioreactors that were constructed prior to and subsequent to the AD process. The proliferating Firmicutes, Bacteroidetes, and Protobacteria were crucial to the AD of RS and LDPE. The three predominant methanogenic genera present in the constructed digesters and inoculum were Methanobacterium, Methanolinea, and Methanosarcina, each with a distinct abundance level. The findings open up the possibility of better understanding the effect of co-digestion of WP and LCB on enhancing CH4 production, which is critical for developing strategies for bioremediation and waste valorization simultaneously with biofuel production.

New insight of combined hydrothermal and ultrasonic pretreatment for methane production from anaerobic digestion of food waste

ABSTRACT Food waste (FW) biotransformation into bioenergy has garnered a lot of scientific interest as a way to address the energy crisis and trash disposal issues. FW is converted into biogas, a gaseous combination of biomethane and carbon dioxide. In order to valorize FW, anaerobic digestion (AD) with combined pretreatment (hydrothermal (HT) and ultrasonic (US)) is used as a potential method. Three digesters were investigated: the control (unpretreated), HT(121°C) + US, and HT(134°C) + US, respectively. Based on changes in the combined pretreatment conditions, the paper assessed the methane productivity. Furthermore, kinetic modeling was evaluated with six kinetic models. The results show that the HT pretreatment at 121°C combined with US improves the volatile solid (VS) removal to 73 ± 5% and the methane yield to 529.7 ± 11 NmL/gVS. Both the Transference model and the first order have the greatest fits in terms of R2, and they also have the best fits in terms of relative errors, and methane production rate, respectively. The combined pretreatment has a positive impact on increasing methane yield as well as stabilizing the anaerobic digestion process.

Characterization and evaluation of the anaerobic treatability of a dairy wastewater.

In this study, the characteristics, anaerobic treatability, and energy potential of wastewater samples taken from a dairy products industry were investigated. It was determined that the wastewater has a high organic load (COD = 2800 mg O2/L) and a large proportion of this load is biodegradable. The biochemical methane potential (BMP) value of wastewater was measured as 1118.71 ± 122 ml CH4/L. Volatile solids (VS) removal of 67.25 ± 4.98% was achieved during batch tests and the obtained methane yield was calculated as 411.59 ± 22.8ml CH4/g VS. Peak methane formation rate and lag time of microorganisms were determined as 163.42 ± 3.83 ml CH4/g VS d and 0.584 ± 0.023 d, respectively. Rate constant for the first-order kinetic model was 0.384 ± 0.072 d-1. The volatile fatty acid (VFA) yield was measured as 155.19 mg COD/g VSS. It was concluded that the wastewater can be treated anaerobically without any inhibition and it has great energy potential. PRACTITIONER POINTS: Dairy wastewater has a large organic load and that most of the organics can be easily biodegradable. Although there are many components considered to be toxic for anaerobic treatment in wastewater, they were found to be very under the inhibition thresholds and did not pose any risk of toxicity. At a satisfactory level, organic matter removal and methane formation were observed in batch anaerobic tests. A rapid microbial adaptation was achieved and the system reached equilibrium in a short time without any acid accumulation. The electrical and caloric energy potentials of the obtained methane gas were calculated as 2.12 and 4.25 kWh/m3, respectively.

Mechanism of ball milling pretreatment to improve the anaerobic digestion performance and energy conversion efficiency of corn straw

In this study, the effects of ball-milling (BM) pretreatment on the anaerobic digestion (AD) performance and energy conversion efficiency of corn straw (CS) were explored. The AD testing was conducted by varying BM times (0–120 min) and TS (4–10 %). The results showed that BM pretreatment increased microbial and enzyme accessibility to the CS and facilitated the hydrolytic acidification process of AD. The peak concentration of volatile fatty acids (VFAs) (5325.69 mg/L) and chemical oxygen demand (COD) (14524 mg/L) were increased, resulting in more substrates available for methanogenic bacteria. The lag phase time was shortened (37.41–56.12 %) and the cumulative methane production was increased (45.63–104.11 %). Accelerated rate of total ammonia nitrogen (TAN) release resulted in increased buffering capacity of the digestion system. Reduced the initial density of the digestive slurry (6.91–9.58 %) and altered the water distribution (maximum increase in free water content to 70.4 %), which facilitated the agitation of the AD process. Excessive BM times (>60 min) and TS (>8%) are not recommended. The BM60-6 presented the highest volatile solids (VS) removal (78.79 %), cellulose degradation (92.07 %) and biochemical methane potential (BMP) (309.69 mL/g VS). The BM pretreatment also improved the rheological characteristics of digestive slurry and reduced the stirring power consumption of the AD process. The BM60-6 showed the largest net energy benefit (28.2101 KJ/g VS) and net residual value (0.5000), and the high energy input of the pretreatment was balanced. This discovery breaks the conventional wisdom that mechanical pretreatment is meaningless because of higher power consumption.

Enhancing kitchen waste anaerobic digestion by recycled aluminum industry waste: Alkali treatment and potential electron transfer mechanism

Kitchen waste has become a significant environmental concern worldwide. Red mud, an industrial solid waste characterized by its porous structure and high iron oxide content, exhibits potential as a conductive conduit in the direct interspecies electron transfer (DIET) pathway. In this study, red mud pretreatment of kitchen waste was conducted to enhance anaerobic digestion (AD). The effect and mechanism of enhancing kitchen waste AD by red mud pretreatment was studied for the first time. Results indicated that red mud pretreatment could accelerate the hydrolysis of organic compounds and alleviate the acid inhibition. Consequently, the methane production rate was increased from 260.7 mL/g VS to 402.3 mL/g VS, i.e., up to 54.3%. And volatile solids removal efficiency was increased from 53.9% to 73.1%, i.e., up to 35.6%. Furthermore, microbial community analysis revealed the enrichment of electrochemically active bacteria (Synergistaceae), acetogenic bacteria (Syntrophomonadaceae) and methanogens (Methanobacterium and Methanosarcina), which played essential roles in interspecies hydrogen transfer (IHT) and DIET. This study showed that red mud pretreatment has the potential to enhance kitchen waste AD which contributes to carbon mitigation. It also threw the potential new insights to the relative mechanism.

Effects of Short Retention Times and Ultrasound Pretreatment on Ammonium Concentration and Organic Matter Transformation in Anaerobic Digesters Treating Sewage Sludge

Anaerobic digestion of sewage sludge is limited at the hydrolysis stage of the process. The goal of this study was to assess the effects of sludge retention times and ultrasound pretreatment on the ammonium concentration and organic matter transformation in anaerobic digesters treating sewage sludge. To achieve this, two laboratory-scale semicontinuous anaerobic digesters were operated for a period of over 70 d, including a control reactor and another fed by pretreated sludge. Both anaerobic systems were fed with mixed sludge (50%/50% primary/secondary treatment) in mesophilic conditions (37 °C), with solid retention times (SRT) of 7.5 d (Phase I) and 3 d (Phase II). The performance of the anaerobic digestion process was assessed in terms of the methane yield and the total and soluble chemical organic demand, total solids, and volatile solids removal. The results showed that the ultrasound pretreatment caused an increase of around 22.2% in CODt removal for an SRT of 7.5 d. Meanwhile, an SRT of 3 d resulted in a decrease of up to 92.4% in CODt removal. The performance in terms of biogas production and organic matter removal was significantly affected by the SRT reduction to 3 d, showing that the process is not viable in these conditions.