Higher Soluble Chemical Oxygen Demand Research Articles

Anaerobic bio-methane potential of the liquors from hydrothermal carbonization of different lignocellulose biomasses

In this work, the spent liquor of pine sawdust (L1), canola oil waste (L2), olive oil waste (L3) and vineyards waste (L4) from hydrothermal carbonization (220 °C, 1 h) process were studied as substrates for biogas production. Kinetic degradation using three kinetic models (Gompertz model, Hill model and Chapman model) was also analyzed. The batch experiments showed that the highest methane yield (253 NmLCH4/gCODadded) and higher soluble Chemical Oxygen Demand (sCOD) removal efficiency (71%) was achieved for the spent liquor of L1, reaching up to 81% of the theoretical methane yield. The liquid fractions of L2, L3 and L4 resulted in lower yields (24 ̶ 36% of the theoretical yield) and lower sCOD removal (40 ̶ 45%), which can be related to the presence of recalcitrant nitrogen materials formed during the HTC. Gompertz model better represents the performance of the liquor fractions (L1 and L2), having long lag phase (5–7 days), while Chapman model adjusted the accuracy of the behavior of L3 and L4 (lag phase < 1 days). As a conclusion, the spent liquor coming from HTC process of lignocellulosic biomass waste can be used as resource to recover energy through anaerobic digestion.

Does the combined free nitrous acid and electrochemical pretreatment increase methane productivity by provoking sludge solubilization and hydrolysis?

Free nitrous acid based pretreatments are novel and effective chemical strategies for enhancing waste activated sludge solubilization. In this study, the synergetic effects of the combined free nitrous acid and electrochemical pretreatment on sludge solubilization and subsequent methane productivity were evaluated. The results indicated that pretreatment with 10 V plus 14.17 mg N/L substantially enhanced sludge solubilization, with the highest soluble chemical oxygen demand concentration of 3296.7 mg/L, 25.6-time higher than that without pretreatment (128.9 mg/L). Due to the potential toxicity of NO2− and NO3− to microorganisms and its bioprocesses, the methane production of sludge pretreated by free nitrous acid was significantly deteriorated. The maximum methane yield (152.0 ± 9.6 mL/g-VSadded) was observed at 10 V pretreatment alone, only 1.7% higher than that of the control (149.4 ± 1.6 mL/g-VSadded). Combined pretreatment indeed enhances the sludge solubilization and hydrolysis, but does not always induce an improved anaerobic digestion efficiency.

Coagulation-flocculation and moving bed biofilm reactor as pre-treatment for water recycling in the petrochemical industry.

Water recycling and reuse is of important value in water-using sectors like petrochemical industry. The aim of this research was to optimise the pre-treatment of petrochemical wastewater to undergo a further membrane treatment, with the final objective of water recycling within the same industry. Laboratory coagulation-flocculation tests prior to biological treatment were performed using Actiflo® Veolia commercial technology and an optimal coagulant dose of 30 mg/L ferric chloride was obtained. A bench-scale Moving Bed Biofilm Reactor (MBBR) system with two sequential reactors with working volumes of 5 L was filled with Z-carriers at 35% of their working volume. Organic loading rate (OLR) was varied from 0.2 to 3.25 kg/(m3 d) and the hydraulic retention time (HRT) ranged from 23.4 h to 4.5 h. High soluble chemical oxygen demand (sCOD) removals were obtained in stationary states (80-90%) and the calculated maximum sCOD that the system could degrade was 4.96 ± 0.01 kg/(m3 d) at 23 ± 2 °C. Changes in feed composition did not decrease sCOD removals showing that MBBR is a robust technology and the coagulation-flocculation step could be by-passed. Further removal of total suspended solids (TSS) and turbidity from the MBBR effluent would be required before a reverse osmosis (RO) step could be performed. A biofilm-forming genus, Haliscomenobacter spp., and an oil degrading genus Flavobacterium spp. were found in all the attached biomass samples. Acinetobacter spp. was the major bacterial genera found in suspended biomass. Proteobacteria and Bacteroidetes were the major phyla detected in the carrier samples while Proteobacteria the main one detected in the suspended biomass. The lack of fungal annotated sequences in databases led to a major proportion of fungal sequences being categorized as unclassified Fungi. The results obtained indicate that MBBR is an appropriate technology for hydrocarbon-degrading microorganism growth and, thus, for petrochemical wastewater pre-treatment for water regeneration.

Bioelectrochemically-assisted vermibiofilter process enhancing stabilization of sewage sludge with synchronous electricity generation

Bioelectrochemically-assisted vermifilter (VBFBE) with sewage sludge as the anode fuel was constructed to accelerate composting of sewage sludge, which could increase the quality of the compost and harvest electric energy in comparison with vermicomposting and electrochemical only. Results revealed that the sludge stabilization with a higher soluble chemical oxygen demand (SCOD) and lower NH4+-H during 40 days of composting. At the composting, pH, C/N, electrical conductivity (EC) and germination index (GI) results demonstrated that the maturity degree of VBFBE4 was higher than that of other VBFBE. The VBFBE4 yielded a voltage of 1.024 V and maximum power density of 105.28 mW/m2 on 3th day. The bacteria in VBFBE4 were richer and higher in terms of diversity than those in other VBFBE, that was demonstrated that combination vermicomposting and electrochemistry could improve the sludge stabilization degree, accelerate sludge composting process and enhance composting maturity.

Synergetic pretreatment of algal biomass through H2O2 induced microwave in acidic condition for biohydrogen production

The objective of the present study is to improve the biohydrogen production from marine macroalgae (Ulva reticulate) by acidic - hydrogen peroxide (H2O2) induced microwave (AHMW) pretreatment. Higher soluble chemical oxygen demand (SCOD) release of 1450 mg/L and its liquefaction rate of 30.2% was achieved in microwave (MW) pretreatment with treatment time period of 15 mins. Varying concentration of H2O2 from 0.003 to 0.03 g/g TS were used in the optimal microwave power (40%) to enhance the organic release in H2O2 induced microwave pretreatment (HMW). Maximum liquefaction of 33.9% was obtained at the H2O2 concentration of 0.024 g /g TS. The combined HMW pretreatment under acidic (pH 4–6.5) show synergistic effect on organic release. At optimal pH 5, AHMW pretreatment shows the SCOD release of 1850 mg/L with its liquefaction of 38.5% at time of 10 min. Therefore, AHMW pretreatment significantly reduce the treatment time and increase liquefaction when compared to MW and HMW. The maximum biohydrogen production was observed as 92.5 mL H2/g COD in AHMW pretreatment.

The role of cosubstrate and mixing on fungal biofilm efficiency in the removal of tannins

ABSTRACT Tannins are polyphenolic compounds produced by plants and they are used in industrial vegetable tanning of leather. Tannins represent one of the low biodegradability substances in tannery wastewaters with high recalcitrant soluble chemical oxygen demand, furthermore high concentration of tannins can inhibit biological treatment. In the present study, four novel rotating submerged packed bed reactors were inoculated with a selected fungal strain to reach a biological degradation of tannins in non-sterile conditions. The selected fungal strain, Aspergillus tubingensis MUT 990, was immobilised in polyurethane foam cubes carriers and inserted inside a submerged rotating cage reactors. The reactors were feed with a solution composed of four tannins: Quebracho (Schinopsis spp.), Wattle (Mimosa spp.), Chestnut (Castanea spp.) and Tara (Caesalpinia spp.). Four reactors with a volume of 4 L each were used, the co-substrate was pure malt extract, the hydraulic retention time was 24 h and the pH setpoint was 5.5. The reactors configuration was chosen to allow the study of the effect of rotation and the co-substrate addition on tannins removal. The experiment lasted two months and it was achieved 80% of chemical oxygen demand and up to 90% dissolved organic carbon removal, furthermore it was detected an important tannase activity.

Microwave enhanced advanced oxidation treatment of dairy manure

The microwave enhanced advanced oxidation process (MW-AOP) was used to treat dairy manure in a continuous-flow 915 MHz microwave wastewater treatment system. The treatment efficiency increased with an increase in temperature, as well as hydrogen peroxide dosage. The settling property was also improved in all treated sets, regardless of temperature applied. The system operated at temperatures >100 °C had a much higher soluble chemical oxygen demand than at temperatures <100 °C. The highest soluble carbonaceous compounds, orthophosphate and ammonia were obtained at 110 °C and 0.6%H2O2 per % of total solids content. The process should be operated at higher temperatures and higher hydrogen peroxide dosages for maximizing solids disintegration, nutrient release and energy efficiency. An energy fingerprint correlating the cumulative energy consumption and temperature rise was developed. The results demonstrated that the custom designed MW-AOP system is suitable for the effective treatment of dairy manure. The system can readily be scaled up and integrated into a dairy farm manure treatment and resource recovery system.

Anaerobic co-digestion of sewage sludge and food waste for hydrogen and VFA production with microbial community analysis

In this study, the anaerobic co-digestion of food waste (FW) and sewage sludge (SS) was investigated for the production of hydrogen and volatile fatty acids (VFAs). The results showed that the anaerobic co-digestion of these materials enhanced the hydrogen content by 62.4% (v/v), 29.89% higher than that obtained by FW digestion alone, and the total VFA production reached at 281.84 mg/g volatile solid (VS), a 8.38% increase. This enhancement was primarily resulted from improvements in the multi-substrate characteristics, which were obtained by supplying a higher soluble chemical oxygen demand (23.78–32.14 g/L) and suitable a pH (6.12–6.51), decreasing total ammonia nitrogen by 18.67% and ensuring a proper carbon/nitrogen ratio (15.01–23.01). Furthermore, maximal hydrogen (62.39 mL/g VS) and total VFA production potential (294.63 mg/g VS) were estimated using response surface methodology optimization, which yielded FW percentages of 85.17% and 79.87%, respectively. Based on a pyrosequencing analysis, the dominant bacteria associated with VFA and hydrogen production were promoted under optimized condition, including members of genera Veillonella and Clostridium and the orders Bacteroidales and Lactobacillales.

Microwave enhanced advanced oxidation treatment of municipal wastewater sludge

Three sludge types (primary sludge, secondary sludge, and anaerobic digested sludge) and centrate produced from a local municipal wastewater treatment plant were treated by the microwave enhanced advanced oxidation process. All sludge types exhibited a certain degree of solids solubilization and phosphorus release, as well as altered physical properties after the treatment. The extent of treatment was influenced by the inherent characteristics of sludge itself, besides the treatment process conditions, such as temperature and hydrogen peroxide dosage. The microwave enhanced advanced oxidation process was very effective for the treatment of all types of sludge for purpose of solids solubilisation, and nutrients release for resource recovery. Very high soluble chemical oxygen demand concentrations (62%) and total suspended solids reduction (75%) were obtained in the treated secondary sludge conducted in the pilot-scale continuous-flow system. The microwave enhanced advanced oxidation treatment system shall be used for treating both primary and secondary sludge, and therefore, the system shall be installed in the treatment train after an aerobic biological treatment system, and before an anaerobic digestion system to gain the maximum process efficiency.

Improved process performance of the acidification phase in a two-stage anaerobic digestion of complex organic waste: Effects of an iron oxide-zeolite additive

Improvement of the acidification phase is an attractive alternative to break through the rate-limiting step in the two-phase anaerobic digestion of complex organic wastes. An additive named iron oxide-zeolite was introduced into the acidification phase at mesophilic and room temperature. By virtue of the additive supplemented, significantly improved hydrolysis/fermentation in regard to higher soluble chemical oxygen demand (sCOD) concentration (21.53–27.30%) and better lignocellulosic degradation at both temperatures has been obtained. Furthermore, an optimized volatile fatty acid formation type (more favorable acetate and less undesired propionate) has been achieved. The favorable environment of the acidogenic effluent facilitated the subsequent methanogenesis. The increased microbial community abundances of some hydrolytic, acetogenic and cellulolytic bacteria may provide the explanation on the promoted hydrolysis/acidogenesis. The results in this study suggested that supplementation of the iron oxide-zeolite into the acidification phase is a valuable alternative to improve hydrolysis/acidogenesis of the complex substrates.

Enhanced biogas production from anaerobic co-digestion of pig slurry and horse manure with mechanical pre-treatment

ABSTRACTEnhanced biogas production from anaerobic co-digestion of pig slurry and horse manure with mechanical pre-treatment. In this study, co-digestion of horse manure and pig slurry was investigated in a continuously stirred tank reactor, with a mechanical pre-treatment. Experiments were conducted at 37°C, with hydraulic retention times of 23 days and increasing shares of horse manure, corresponding to different horse manure to pig slurry ratios (HM:PS) equal to 0:100, 10:90, 13:87 and 20:80, in terms of percentage of inlet volatile solids (%VS inlet). The results show that the best synergetic effect between the microbial consortia of pig slurry and the high Carbon to Nitrogen ratio (C/N) of horse manure is obtained for the mixture of 20:80%VS inlet, yielding the highest specific methane production (SMP = 142.6 L kgTCOD−1) and the highest soluble chemical oxygen demand (SCOD) reduction (68.5%), due to the high volatile dissolved solids content and soluble chemical oxygen demand to total chemical oxygen demand ratio (SCOD/TCOD). Thus, co-digestion of horse manure and pig slurry is shown to be a promising approach for biogas production and as a waste treatment solution. Furthermore, the analysis provides a methodology for the pre-treatment of these substrates and to investigate into the best combination for improved biogas production.

Enhanced granulation and methane recovery at low load by downflow sludge circulation in anaerobic treatment of domestic wastewater

The effects of downflow sludge circulation on granulation and methane recovery at low load were investigated for domestic wastewater treatment in a modified anaerobic reactor. Compared with conventional upflow anaerobic reactors, enhanced granulation with shortened start-up time was achieved and stable granules were successfully cultivated only after 58 days operations. The introduction of downflow sludge circulation resulted in reverse wastewater-sludge flow and uniform sludge distribution in the reaction zone, which contributed to enhanced wastewater-sludge mass transfer and satisfactory performance with a high soluble chemical oxygen demand (SCOD) removal efficiency of 94.8% at hydraulic retention time (HRT) 6 h. Besides, enhanced liquid-to-gas mass transfer caused a lower dissolved CH4 saturation index of 1.11 and a higher CH4 recovery efficiency of 79.48% at HRT 6 h. High throughput sequencing revealed a distinct shift of microbial community during start-up period from Proteobacteria to Bacteroidetes and Chloroflexi in the existence of downflow sludge circulation.

Volatile Fatty Acid Accumulation by Alkaline Control Strategy in Anaerobic Fermentation of Primary Sludge

Abstract Effects of pH (5–12) on primary sludge (PS) fermentation and volatile fatty acid (VFA) accumulation were studied in batch experiments. Results showed that under strong alkaline conditions (pH 10–12), hydrolysis could be accelerated and high soluble chemical oxygen demand (SCOD) produced, but acidification was inhibited, resulting in a decrease of VFA production; whereas in weak base (pH 8, 9) conditions, more VFAs accumulated, although less SCOD was produced. Optimal conditions for PS to accumulate VFAs in this study were pH 9 and a fermentation time of 10 days. The study also revealed that protein degradation played an important role in VFA production. More protein was hydrolyzed and acidified at pH 9 than at pH 10 in the system, although protein content at pH 10 was higher. Acetic and propionic acids were the dominant acid species. Furthermore, a comparison of VFAs, NH4+, and pH relationships in pH 9 and pH-uncontrolled systems showed that weak base conditions could significantly enhance the pr...

Anaerobic fermentation combined with low-temperature thermal pretreatment for phosphorus-accumulating granular sludge: Release of carbon source and phosphorus as well as hydrogen production potential

Releases of organic compounds and phosphorus from phosphorus-accumulating granular sludge (PGS) and phosphorus-accumulating flocculent sludge (PFS) during low-temperature thermal pretreatment and anaerobic fermentation were investigated. Meanwhile, biogas production potential and microbial community structures were explored. The results indicate that much more soluble chemical oxygen demand (SCOD) and phosphorus were released from PGS than from PFS via low-temperature thermal pretreatment because of the higher extracellular polymeric substances (EPS) content in PGS and higher ratio of phosphorus reserved in EPS. Furthermore, PGS contains more anaerobes and dead cells, resulting in much higher SCOD and volatile fatty acids release from PGS than those from PFS during fermentation. PGS fermentation facilitated the n-butyric acid production, and PGS exhibited the hydrogen production potential during fermentation due to the presence of hydrogen-producing bacteria. Therefore, anaerobic fermentation combined with low-temperature thermal pretreatment can facilitate the recovery of carbon and phosphorus as well as producing hydrogen from PGS.

Continuous‐flow microwave enhanced oxidation process for treating sewage sludge

AbstractThe microwave‐enhanced advanced oxidation (MW/H2O2‐AOP) treatment of sewage sludge in a continuous‐flow 915 MHz microwave system was studied. A higher H2O2 dosage at the same flow rate resulted in better solids disintegration in terms of higher soluble chemical oxygen demand. The highest soluble chemical oxygen demand concentration of 5174 mg/L was obtained at a dosage of 0.005 L/L (0.5 % v/v). A higher soluble chemical oxygen demand was obtained at a higher flow rate with the same H2O2 dosage. A substantial amount of soluble phosphorus (over 60 % of total phosphorus content) was produced for all treatments, regardless of H2O2 dosage. A first‐order reaction kinetics of soluble chemical oxygen demand was proposed in this study. Real‐time energy consumption corresponding to performance efficacy, which provides a realistic assessment of the process efficiency, was calculated. Energy consumption was found to vary between 0.22–0.29 kWh/L of sludge treated. The results demonstrated that a continuous‐flow 915 MHz microwave system resulted in high treatment efficiency in terms of nutrient release, solids disintegration, and low energy consumption, which is suitable for real‐time industrial applications.

Enhancement of Aerobic Wastewater Treatment by the Application of Attached Growth Microorganisms and Microbubble Generator

This paper presents the efficiency improvement in aerobic wastewater treatment technology through the application of a microbubble generator (MBG) for aeration. Aeration using an MBG is accomplished through water circulation and does not need air compressors, making it more energy efficient than conventional aerators. The MBG aerobic system with the variations on liquid flow rate (Q1) and airflow rate (Qg) combination was tested using artificial wastewater with a typical composition of organic waste. Experimental data were evaluated by means of a simplified mathematical model to systematically compare different MBG schemes. The study confirmed that the soluble chemical oxygen demand (SCOD) removal efficiency was significantly affected by the Qg values. Lower Qg values were preferable because they tended to have higher soluble chemical oxygen demand (SCOD) removal efficiency. However, the microbubbles were less stable at lower Qg due to the high incidence of bubble collisions. The study concluded that for applications in an actual aerobic waste treatment pond, the positioning of the MBG in the pond had to be carefully designed to minimize the collision tendency.

Enhanced mesophilic anaerobic digestion of food waste by thermal pretreatment: Substrate versus digestate heating

Food waste (FW) represents a source of high potential renewable energy if properly treated with anaerobic digestion (AD). Pretreating the substrates could yield a higher biomethane production in a shorter time. In this study, the effects of thermal (heating the FW in a separate chamber) and thermophilic (heating the full reactor content containing both FW and inoculum) pretreatments at 50, 60, 70 and 80°C prior to mesophilic AD were studied through a series of batch experiments. Pretreatments at a lower temperature (50°C) and a shorter time (<12h) had a positive effect on the AD process. The highest enhancement of the biomethane production with an increase by 44–46% was achieved with a thermophilic pretreatment at 50°C for 6–12h or a thermal pretreatment at 80°C for 1.5h. Thermophilic pretreatments at higher temperatures (>55°C) and longer operating times (>12h) yielded higher soluble chemical oxygen demand (CODs), but had a negative effect on the methanogenic activity. The thermal pretreatments at the same conditions resulted in a lower solubilization of COD. Based on net energy calculations, the enhanced biomethane production is sufficient to heat up the FW for the thermal, but not for the thermophilic pretreatment.

Radiofrequency-oxidation treatment of sewage sludge

A novel thermal–chemical treatment technology using radiofrequency heating and oxidants (hydrogen peroxide, ozone and a combination of both) was used for the treatment of sewage sludge. This was to evaluate the process effectiveness on cell disintegration and nutrient release of sludge, physical property changes such as particle size distribution, dewaterability and settleability, and their inter-relationships. The effectiveness of treatment processes was in the following order, from the most to least: thermal–oxidation process, oxidation process and thermal process. The thermal–oxidation process greatly increased cell disintegration and nutrient release, improved settleability, and decreased particle sizes. The treatment scheme involving ozone addition followed by hydrogen peroxide and radiofrequency heating yielded the highest soluble chemical oxygen demand, volatile fatty acids, ammonia and metals, while proffering the shortest capillary suction time and excellent settling properties.

Effects of temperature on hydrolysis performance and short-chain fatty acids production during thermophilic micro-aerobic fermentation of waste activated sludge

Rapid hydrolysis of waste activated sludge (WAS) can be achieved by improving activities of extracellular enzymes under proper temperature conditions. As short-chain fatty acids (SCFAs) accumulation is always consumed by methanogens under anaerobic conditions, and considering that the micro-aerobic condition can inhibit the activities of methanogens, in this study, effects of temperature (55–75°C) on thermophilic micro-aerobic fermentation of WAS were investigated. Results showed that the highest soluble chemical oxygen demand (SCOD) yield was obtained at 60°C (4,407 ± 80 mg/L, 36 h), 2.0 times higher than that obtained at 75°C (2,180 ± 40 mg/L, 36 h), the corresponding hydrolysis rate was 0.6689 d−1. The highest SCFAs yield was 2,928 ± 12 mg COD/L at 60°C and 36 h, 4.9 times higher than that obtained at 75°C (594 ± 10 mg COD/L, 36 h). The analysis of SCFAs composition showed that acetic acid (HAc) accounted for the most percentage (>40%), followed by n-valeric (n-HVa) (20–25%), and propionic acids (HPr) (10–15%). Total suspended solids removal efficiency reached 18.7% after 192-h fermentation at 60°C. These results suggested that the optimal thermophilic micro-aerobic conditions for WAS hydrolysis and SCFAs accumulation from WAS were 60°C and 36-h fermentation time.

Multivariate analysis of sludge disintegration by microwave–hydrogen peroxide pretreatment process

Microwave irradiation (with H2O2) has been shown to offer considerable advantages owing to its flexible control, low overall cost, and resulting higher soluble chemical oxygen demand (SCOD); accordingly, the method has been proposed recently as a means of improving sludge disintegration. However, the key factor controlling this sludge pretreatment process, pH, has received insufficient attention to date. To address this, the response surface approach (central composite design) was applied to evaluate the effects of total suspended solids (TSS, 2–20g/L), pH (4–10), and H2O2 dosage (0–2w/w) and their interactions on 16 response variables (e.g., SCODreleased, pH, H2O2remaining). The results demonstrated that all three factors affect sludge disintegration significantly, and no pronounced interactions between response variables were observed during disintegration, except for three variables (TCOD, TSSremaining, and H2O2 remaining). Quadratic predictive models were constructed for all 16 response variables (R2: 0.871–0.991). Taking soluble chemical oxygen demand (SCOD) as an example, the model and coefficients derived above were able to predict the performance of microwave pretreatment (enhanced by H2O2 and pH adjustment) from previously published studies. The predictive models developed were able to optimize the treatment process for multiple disintegration objectives.