Development of appropriate technology for treatment of molasses-based wastewater

Effect of formic acid inflow on microbial properties of the anaerobic granular sludge in a UASB reactor

In the production of natural rubber, formate or acetate is added to the latex solution to coagulate the rubber; therefore, the wastewater contains high concentrations of organic acids, requiring the application of anaerobic treatment technology. In this study, a two-phase continuous flow experiment using a laboratory-scale upflow anaerobic sludge blanket (UASB) was conducted to investigate the influence of formate inflow on the microbial and physical characteristics of the retained granular sludge. In phase 1, acetate-based wastewater was used as feed, while in phase 2, formate-based wastewater was used as feed. In phase 1, the UASB exhibited high COD removal efficiency (97.2%); in addition, the retained sludge showed increased methane production from acetate and proliferation of acetate-utilizing Methanosaeta species. In phase 2, the UASB performed as well as phase 1, with 98.2% COD removal efficiency. Microbial community structure analysis confirmed that relatives of Methanobacterium formicicum present in the retained sludge were responsible for the degradation of formate in phase 2. However, decreased diameter and slight deterioration of granular sludge settleability were observed. In conclusion, formate inflow has low risk of interference with the process performance of the UASB, but it has negative effects on the physical properties of the granular sludge.

Reuse-focused selection of appropriate technologies for municipal wastewater treatment: a multi-criteria approach

Wastewater treatment technologies (WWTTs) are employed across the world, and the selection is mainly based on 'past experiences' aimed at 'pollution prevention' in the receiving water bodies. This paper aims to develop a methodology for the selection of an appropriate wastewater treatment chain that produces effluent suitable for the defined reuse. Adopting the least weighted cost approach, four decision criteria: Capital cost, Operation and Maintenance cost, Land requirement, and Energy requirement, have been used and the Full Consistency Method (FUCOM) has been employed for obtaining weights. Quality expectations for 14 reuses have been enlisted, and 25 WWTTs have been evaluated in a total of 360 combinations. In Kanpur city, for water reuse in industrial cooling under restricted land and challenging influent quality conditions, a combination of Membrane Bioreactor (MBR) with Wuhrmann process (WP) is obtained as the most preferred suggestion. For non-potable domestic reuse, Anaerobic Anoxic Oxic (A2O) with Ultrafiltration (UF) and Reverse Osmosis (RO) is the most preferred combination. In Varanasi city, for vehicular washing operations and for flow augmentation (inland surface water), under energy-constraint scenario, high-rate activated sludge-based biological filtration and oxygenated reactor (BIOFOR-F) is suggested. For technology supplementation to existing ASP-based STPs in the city to obtain effluent for inland surface water augmentation, WP in combination with microfiltration (MF) and reverse osmosis (RO) is suggested. Thus, the developed model may be used as a decision-making tool for planning a reuse-focused water reclamation program or for upgradation of existing STPs as per resource availability and target reuse objectives.

Effects of hydraulic retention time on biohythane production via single-stage anaerobic fermentation in a two-compartment bioreactor

Hythane has been well known as a mixture of hydrogen and methane gases but their production is mostly in a different way. The present study dealt with the potential biohythane production in a two-compartment (lower, hydrogenesis; upper, methanogenesis) reactor via a single-stage anaerobic fermentation at mesophilic temperature. The effect of hydraulic retention time (HRT) was tested at 10-2 d using food waste substrate. HRT 2 d resulted in (1) maximum removal efficiencies for COD, carbohydrate, lipid and protein contents with values of 58.5, 58.4, 62.6 and 79.1%, respectively; (2) peak hydrogen and methane production rates of 714 and 254 mL/L-d, respectively; and (3) biogas contents of hydrogen 8.6% and methane 48.0% in the produced gas. At this HRT, Clostridium sensu stricto 2 and Methanosaeta were dominant species in H₂ and CH₄ compartments, respectively. The novelty of this work is creating a novel two-compartment reactor for single-stage anaerobic biohythane fermentation.

A full-scale study of external circulation sludge bed (ECSB) system for anaerobic wastewater treatment in a whiskey distillery

Waste liquid streams from distillery were a hurdle in conventional wastewater treatment due to extreme high chemical oxygen demand (COD) and fluctuating feed conditions. A recently commissioned full-scale external circulation sludge bed (ECSB) was applied at a malt whiskey distillery in northeast Taiwan. Start-up of the new ECSB system, which has a total volume of 490 m³ with diameter of 6.55 m (ø) and height of 15.9 m (H), was performed by gradual increasing influent flow rates from zero to the design value of 300 m³ day^-1 in the first 90 days. In the subsequent 204 days, both influent flow rates (0-389 m³ day^-1) and COD concentrations (2.8-18.1 kg L^-1) were highly fluctuated due to diverse batches from the distillery. However, effective bioremediation (COD removal 95.1 ± 2.4%) and biogas production (1195 ± 724 L day^-1) were achieved in this system. Intensively, the Imhoff tests were carried out and shown the settled solids concentration by 0.5 ± 0.4 mL L^-1, while size distributions of granular sludge were analyzed and observed by SEM-EDS. In addition, developments of the anaerobic systems (including lab, pilot, and full scale from the simplest reactor to the latest ECSB) applied in whiskey wastewater treatment were reviewed with their operational parameters for comparing performances of various anaerobic systems. In general, real-time monitoring and feasible operation strategies were critical to successfully run the system by producing clean energy simultaneously. It provides more economically attractive and sustainable-to-adopt ECSB not only an end-of-pipe process but also a bioresource technology.

Evaluation of process performance and retained sludge properties of a psychrophilic UASB reactor for treatment of iso-plophyl alcohol (2-propanol)-containing wastewater

In this study, a continuous feeding experiment was conducted with synthetic iso-plophyl alcohol (2-propanol)-containing wastewater using a lab-scale psychrophilic UASB reactor to evaluate process performance and retained sludge properties. For smooth acclimation, methanogenic granular sludge was seeded and a proportion of 2-propanol in the synthetic wastewater containing sucrose and volatile fatty acids was increased stepwise from 0% to 30%, 60% and then 90% of COD (chemical oxygen demand). As a result, after a 4-week period for acclimation to 2-propanol degradation, a COD removal rate of 95% was achieved at an organic loading rate (OLR) of 8.4 kg COD/m³/day. Additionally, the physical properties of the retained granular sludge were maintained even when the reactor was supplied with 2-propanol-rich wastewater for more than 200 days. From the batch assays using serum bottles, methanogenic degradation of 2-propanol was observed with acetone accumulation. By comparison, 2-propanol degradation was clearly inhibited in the presence of chloroform as a specific inhibitor of methanogen. A domain archaeal community structure analysis targeting 16S rRNA genes showed the relative abundance of the genus Methanospillium was increased in the 2-propanol acclimated sludge. These results suggested Methanospillium related species in the granular sludge appreciably contributed to the direct degradation of 2-proapanol into acetone under an anaerobic condition.

Influence of tetramethylammonium hydroxide (TMAH) on the microbial properties of anaerobic granular sludge acclimated to isoplophyl alcohol (IPA) wastewater under psychrophilic conditions

In this study, a continuous flow experiment was conducted in which a lab-scale upflow anaerobic sludge blanket (UASB) reactor at psychrophilic conditions (18-19°C) was fed with artificial wastewater, containing tetramethylammonium hydroxide (TMAH) and isoplophyl alcohol (IPA), from the electronics industry. This was done to evaluate process performance and microbial properties of the granular sludge that was retained in the reactor. The inoculated granular sludge was precultured with IPA containing wastewater but not TMAH; as a result, no degradation was observed in 30 days of operation. To enhance degradation, the reactor was seeded with 2% weight of the TMAH-enriched sludge, after which TMAH was enhanced. Consequently, the total COD removal efficiency reached 90% at an organic loading rate of 7.5 kg COD/m³/day. The TMAH inflow decreased the diameter of the retained granular sludge, but the sludge retained its settleability. The proliferation of the Methanometylovorans microorganisms present in the enrichment culture was confirmed by analysis of the 16 S rRNA gene in the retained sludge. In addition, TMAH degradation was inhibited by addition chloroform, a methanogen inhibitor. These results suggested species in the genus Methanometylovorans in the granular sludge contributed significantly to methanogenic TMAH degradation.

Microbial community redundancy in anaerobic digestion drives process recovery after salinity exposure

Anaerobic digestion of high-salinity wastewaters often results in process inhibition due to the susceptibility of the methanogenic archaea. The ability of the microbial community to deal with increased salinity levels is of high importance to ensure process perseverance or recovery after failure. The exact strategy of the microbial community to ensure process endurance is, however, often unknown. In this study, we investigated how the microbial community is able to recover process performance following a disturbance through the application of high-salinity molasses wastewater. After a stable start-up, methane production quickly decreased from 625 ± 17 to 232 ± 35 mL CH₄ L^-1 d^-1 with a simultaneous accumulation in volatile fatty acids up to 20.5 ± 1.4 g COD L^-1, indicating severe process disturbance. A shift in feedstock from molasses wastewater to waste activated sludge resulted in complete process recovery. However, the bacterial and archaeal communities did not return to their original composition as before the disturbance, despite similar process conditions. Microbial community diversity was recovered to similar levels as before disturbance, which indicates that the metabolic potential of the community was maintained. A mild increase in ammonia concentration after process recovery did not influence methane production, indicating a well-balanced microbial community. Hence, given the change in community composition following recovery after salinity disturbance, it can be assumed that microbial community redundancy was the major strategy to ensure the continuation of methane production, without loss of functionality or metabolic flexibility.

Process contribution evaluation for COD removal and energy production from molasses wastewater in a BioH2-BioCH4-MFC-integrated system

In this study, a three-stage-integrated process using the hydrogenic process (BioH₂), methanogenic process (BioCH₄), and a microbial fuel cell (MFC) was operated using molasses wastewater. The contribution of individual processes to chemical oxygen demand (COD) removal and energy production was evaluated. The three-stage integration system was operated at molasses of 20 g-COD L^-1, and each process achieved hydrogen production rate of 1.1 ± 0.24 L-H₂ L^-1 day^-1, methane production rate of 311 ± 18.94 mL-CH₄ L^-1 day^-1, and production rate per electrode surface area of 10.8 ± 1.4 g m^-2 day^-1. The three-stage integration system generated energy production of 32.32 kJ g-COD^-1 and achieved COD removal of 98 %. The contribution of BioH₂, BioCH₄, and the MFC reactor was 20.8, 72.2, and, 7.0 % of the total COD removal, and 18.7, 81.2, and 0.16 % of the total energy production, respectively. The continuous stirred-tank reactor BioH₂ at HRT of 1 day, up-flow anaerobic sludge blanket BioCH₄ at HRT of 2 days, and MFC reactor at HRT of 3 days were decided in 1:2:3 ratios of working volume under hydraulic retention time consideration. This integration system can be applied to various configurations depending on target wastewater inputs, and it is expected to enhance energy recovery and reduce environmental impact of the final effluent.

High salinity in molasses wastewaters shifts anaerobic digestion to carboxylate production

Biorefinery wastewaters are often treated by means of anaerobic digestion to produce biogas. Alternatively, these wastewaters can be fermented, leading to the formation of carboxylates. Here, we investigated how lab-scale upflow anaerobic sludge blanket reactors could be shifted to fermentation by changing organic loading rate, hydraulic retention time, pH, and salinity. A strong increase in volatile fatty acid concentration up to 40 g COD L(-1) was achieved through increasing salinity above 30 mS cm(-1), as well as a decrease in methane production by more than 90%, which could not be obtained by adjusting the other parameters, thus, indicating a clear shift from methane to carboxylate production. Microbial community analysis revealed a shift in bacterial community to lower evenness and richness values, following the increased salinity and VFA concentration during the fermentation process. A selective enrichment of the hydrogenotrophic Methanomicrobiales took place upon the shift to fermentation, despite a severe decrease in methane production. Particle size distribution revealed a strong degranulation of the sludge in the reactor, related to the high salinity, which resulted in a wash-out of the biomass. This research shows that salinity is a key parameter enabling a shift from methane to carboxylate production in a stable fermentation process.

High organic loading treatment for industrial molasses wastewater and microbial community shifts corresponding to system development

Molasses wastewater contains high levels of organic compounds, cations, and anions, causing operational problems for anaerobic biological treatment. To establish a high organic loading treatment system for industrial molasses wastewater, this study designed a combined system comprising an acidification tank, a thermophilic multi-stage (MS)-upflow anaerobic sludge blanket (UASB) reactor, mesophilic UASB reactor, and down-flow hanging sponge reactor. The average total chemical oxygen demand (COD) and biochemical oxygen demand removal rates were 85%±3% and 95%±2%, respectively, at an organic loading rate of 42kgCODcrm(-3)d(-1) in the MS-UASB reactor. By installation of the acidification tank, the MS-UASB reactor achieved low H2-partial pressure. The abundance of syntrophs such as fatty acid-degrading bacteria increased in the MS-UASB and 2nd-UASB reactors. Thus, the acidification tank contributed to maintaining a favorable environment for syntrophic associations. This study provides new information regarding microbial community composition in a molasses wastewater treatment system.