Application of immobilized and granular dried anaerobic biomass for stabilizing and increasing anaerobic bio-systems tolerance for high organic loads and phenol shocks

Methane production from anaerobic pre-treatment of municipal wastewater combined with olive mill wastewater: A demonstration study

The advanced anaerobic technology (AAT), developed based on an immobilized high-rate anaerobic reactor, was applied as a pretreatment of municipal wastewater (WW) at Karmiel's treatment plant in Israel. The demonstration-scale AAT (21 m3) system was operated at a flow rate of 100 m3day-1 municipal WW mixed with olive mill wastewater (OMW) (0.5 m3day-1) to simulate the scenario of illegal discharge of agro-industrial WW. The AAT provided a stable performance. Specifically, AAT enabled treating high organic loads (9.3 kg m-3day-1) resulting from OMW discharge by shaving the high peaks of organic content and protecting the subsequent activated sludge process. This system enabled the recovery of a significant part of the organic load by anaerobic biodegradation to produce biogas, shown to be highly dependent on temperature and partly on the organic loading rate. The outcomes indicate that the AAT could tolerate an addition of up to 0.5% OMW to municipal WW by removing more than 50% of the total chemical oxygen demand and 18-47% of polyphenols. This work shows that the AAT system has the potential of pretreating municipal WW, increasing the energy efficiency of the plant, and protecting small-medium WWTPs from sudden agro-industrial discharges.

In-situ biological biogas upgrading using upflow anaerobic polyfoam bioreactor: Operational and biological aspects

A high rate upflow anaerobic polyfoam-based bioreactor (UAPB) was developed for lab-scale in-situ biogas upgrading by H2 injection. The reactor, with a volume of 440 mL, was fed with synthetic wastewater at an organic loading rate (OLR) of 3.5 g COD/L·day and a hydraulic retention time (HRT) of 7.33 h. The use of a porous diffuser, alongside high gas recirculation, led to a higher H2 liquid mass transfer, and subsequently to a better uptake for high CH4 content of 56% (starting from 26%). Our attempts to optimize both operational parameters (H2 flow rate and gas recirculation ratio, which is the total flow rate of recirculated gas over the total outlet of gas flow rate) were not initially successful, however, at a very high recirculation ratio (32) and flow rate (54 mL/h), a significant improvement of the hydrogen consumption was achieved. These operational conditions have in turn driven the methanogenic community toward the dominance of Methanosaetaceae, which out-competed Methanosarcinaceae. Nevertheless, highly stable methane production rates of 1.4-1.9 L CH4/Lreactor.day were observed despite the methanogenic turnover. During the different applied operational conditions, the bacterial community was especially impacted, resulting in substantial shifts of taxonomic groups. Notably, Aeromonadaceae was the only bacterial group positively correlated with increasing hydrogen consumption rates. The capacity of Aeromonadaceae to extracellularly donate electrons suggests that direct interspecies electron transfer (DIET) enhanced biogas upgrading. Overall, the proposed innovative biological in-situ biogas upgrading technology using the UAPB configuration shows promising results for stable, simple, and effective biological biogas upgrading.

Biochemical pathways and enhanced degradation of dioctyl phthalate (DEHP) by sodium alginate immobilization in MBR system

As one of the most representative endocrine disrupting compounds, dioctyl phthalate (DEHP) is difficult to remove due to its bio-refractory characteristic. In this study, an immobilization technology was applied in an MBR system to improve the degradation of DEHP. The degradation efficiency of DEHP was significantly improved and the number of degradation genes increased by 1/3. A bacterial strain that could effectively degrade DEHP was isolated from activated sludge and identified as Bacillus sp. The degradation pathway of DEHP was analyzed by GC-MS. DEHP was decomposed into phthalates (DBP) and Diuretic sylycol (DEP), then further to Phthalic acid (PA). PA was oxidized, dehydrogenated, and decarboxylated into protocatechins, further entered the TCA cycle through orthotopic ring opening. The DEHP degrading strain was immobilized by sodium alginate and calcium chloride under the optimized immobilization conditions, and added to MBR systems. The removal rate of DEHP (5 mg/L) (91.9%) and the number of 3, 4-dioxygenase gene copies was significantly improved by adding immobilized bacteria. Micromonospora, Rhodococcus, Bacteroides and Pseudomonas were the dominant genuses, and the results of bacterial community structure analysis show that immobilization technology is beneficial to system stability. The results showed the potential applications of the immobilized technique in DEHP wastewater treatment in MBR.

Inhibitory effect of phenol on wastewater ammonification

This study aimed to elucidate inhibitory effect of phenol on ammonification of dissolved organic nitrogen (DON) in wastewater. Laboratory incubation experiments were conducted using primary and secondary effluent samples spiked with phenol (100-1000 mg/L) and inoculated with mixed cultures, pure strains of phenol-degrading bacteria (Acinetobacter sp. and Pseudomonas putida F1), and/or an ammonia oxidizing bacterium (Nitrosomonas europaea). DON concentration was monitored with incubation time. Phenol suppressed the ammonification rate of DON up to 62.9%. No or minimal ammonification inhibition was observed at 100 mg/L of phenol while the inhibition increased with increasing phenol concentration from 250 to 1000 mg/L. The inhibition was curtailed by the presence of the phenol-degrading bacteria. DON was ammonified in the samples inoculated with only N. europaea and the ammonification was also inhibited by phenol. The findings suggest that high phenol in wastewater could result in low ammonification and high DON in the effluent.

Al2O3 Nanoparticles Promote the Removal of Carbamazepine in Water by Chlorella vulgaris Immobilized in Sodium Alginate Gel Beads

The roles of Al2O3 nanoparticles on the removal of carbamazepine (CBZ) by Chlorella vulgaris immobilized in sodium alginate gel beads were for the first time investigated. The optimum conditions to prepare immobilized C. vulgaris beads with addition of Al2O3 nanoparticles were determined as follows: C. vulgaris density was 3.0 × 106 cells for 1 mL sodium alginate solution, Al2O3 nanoparticle concentration was 0.5 g/L, and concentrations of sodium alginate and CaCl2 were 1.6% and 1%, respectively. The results showed that the proposed algae beads achieved the highest CBZ removal rate of 89.6% after 4 days of treatment, relative to 68.84%, 48.56%, and 17.76% in sodium alginate-immobilized C. vulgaris, free microalgae, and Al2O3 nanoparticle alginate beads, respectively. The results also showed that the CBZ removal rate increased with more proposed algae beads, while decreased with increased bead diameter. The algae beads exhibited excellent CBZ removal ability even after three recycles. This work provided an economical and effective approach to remove CBZ from water.

Influence of Anaerobic Mesophilic and Thermophilic Digestion on Cytotoxicity of Swine Wastewaters

Recycling wastewater from animal production for fertilizers using anaerobic digestion (AD) is a common method to recover the nutrients in the digestate. However, the digestate toxicity is not well understood because AD is mainly designed for chemical oxygen demand reduction. This study determined the toxicity during AD and the controlling factors with the goal to improve digestate safety during farmer handling to reuse the nutrients. Thermophilic and mesophilic AD of two swine wastewater sources were studied. Mammalian cell cytotoxicity revealed that the effluent after thermophilic digestion was at least 69% more toxic than the mesophilic effluent, owing to higher ammonia and total organic carbon in the former. Ammonia accounted for >55% total cytotoxicity, and the organics of the thermophilic digestate were twice more toxic than those in the mesophilic digestate. Despite less toxicity contribution than the ammonia, the organics did demonstrate significant adverse effects on the thiol-mediated cellular protection mechanism. For swine wastewater nutrient recovery, converting ammonia to less toxic nitrogen forms could lower the toxic hazard of the AD digestate. With much less ammonia, the organics would be the remaining decisive factor for toxicity, which is favorably reduced using thermophilic AD over mesophilic. If the ammonia is not reduced, mesophilic AD would generate a less toxic digestate.

Innovative ex-situ biological biogas upgrading using immobilized biomethanation bioreactor (IBBR)

Biogas, which typically consists of about 50-70% of methane gas, is produced by anaerobic digestion of organic waste and wastewater. Biogas is considered an important energy resource with much potential; however, its application is low due to its low quality. In this regard, upgrading it to natural gas quality (above 90% methane) will broaden its application. In this research, a novel ex-situ immobilized biomethanation bioreactor (IBBR) was developed for biologically upgrading biogas by reducing CO₂ to CH₄ using hydrogen gas as an electron donor. The developed process is based on immobilized microorganisms within a polymeric matrix enabling the application of high recirculation to increase the hydrogen bioavailability. This generates an increase in the consumption rate of hydrogen and the production rate of methane. This process was successfully demonstrated at laboratory-scale system, where the developed process led to a production of 80-89% methane with consumption of more than 93% of the fed hydrogen. However, a lower methane content was achieved in the bench-scale system, likely as a result of lower hydrogen consumption (63-90%). To conclude, the IBBRs show promising results with a potential for simple and effective biogas upgrading.

Effect of anaerobic digester inoculum preservation via lyophilization on methane recovery

A robust anaerobic digestion (AD) inoculum is key to a successful digestion process by providing the abundant bacteria needed for converting substrate to useable methane (CH₄). While transporting digester contents from one AD to another for digester startup has been the norm, transportation costs are high, and it is not feasible to transport wet inoculum to remote locations. In this study, the impact of preservation of AD inoculum via lyophilization was investigated for the purposes of digester startup and restabilization. The effect of lyophilizing inoculum on CH₄ production using food waste as the substrate was tested using biochemical methane potential (BMP) tests under the following conditions: (1) three inoculum sources, (2) two inoculum to substrate ratios (ISR), (3) two cryoprotectants, and (4) two inoculum growth phases. After lyophilization with skim milk, the three inocula produced 144-146 mL CH₄/g volatile solids (VS) and 194-225 mL CH₄/g VS at a 2:1 and 4:1 ISR, respectively, with 33-57% more CH₄ at the 4:1 ISR. Preservation with 10% skim milk exhibited complete recovery of CH₄ production, while 10% glycerol and 10% glycerol/skim milk mixture yielded 76% and 4% CH₄ recovery, respectively. Inoculum growth phase before preservation (mid-exponential or stationary growth phase) did not significantly affect CH₄ recovery. The study indicates that inoculum can be preserved via lyophilization using 10% skim milk as a cryoprotectant and reactivated for food waste digestion. The results provide a systematic quantification of the conditions needed to successfully preserve a mixed AD inoculum.

Acclimation strategy to increase phenol tolerance of an anaerobic microbiota

A wide variety of inhibitory substances can induce anaerobic digester upset or failure. In this work the possibility to improve the resistance of an anaerobic microbiota to a common pollutant, the phenol, was evaluated in a lab-scale semi-continuous bioreactor. An acclimation strategy, consisting in a regular step-wise adaptation of the microbiota to stressful condition was employed. Degradation performances were monitored and molecular tools (16S sequencing and ARISA fingerprinting technique) were used to track changes in the microbial community. The acclimation strategy progressively minimized the effect of phenol on degradation performances. After 3 successive disturbance episodes, microbiota resistance was considerably developed and total inhibition threshold increased from 895 to 1942mg/L of phenol. Microbiota adaptation was characterized by the selection of the most resistant Archaea OTU from Methanobacterium genus and an important elasticity of Bacteria, especially within Clostridiales and Bacteroidales orders, that probably enabled the adaptation to more and more stressful conditions.