Wastewater biofilm formation on self-assembled monolayer surfaces using elastomeric flow cells.

In anaerobic wastewater treatment, microbial biofilm is beneficial for efficient substrate utilization and for preventing the wash-out of key microorganisms. By providing solid supports, biofilm formation can be accelerated due to the early initial adhesion of residing microbes. Alteration in surface properties is therefore one such approach that helps us understand microbial interfacial interaction. Here, self-assembled monolayers of alkanethiols with carboxyl (-COOH), hydroxyl (-OH), and amine (-NH2) terminal moieties on gold (Au) substrates were employed to study the initial adhesion of wastewater microbes. An elastomeric flow cell was also utilized to simulate the environment of wastewater bioreactor. Results from fluorescence in situ hybridization (FISH) portrayed more enhanced microbial adhesion after 2 h on -NH2 functional group with the calculated surface coverage of 12.8 ±â€¯2.4% as compared to 7.7 ±â€¯1.6% on -COOH, 11.0 ±â€¯2.0% on -OH, and 1.2% on unmodified Au surfaces. This might be because of concomitant electrostatic attraction between negatively-charged bacteria and positively-charged (-NH3+) functional groups. Nevertheless, the average surface coverage by individual biofilm clusters was 28.0 ±â€¯5.0 µm2 and 32.0 ±â€¯9.0 µm2 on -NH2 and -OH surfaces, respectively, while -COOH surfaces resulted in higher value (60.0 ±â€¯5.0 µm2) and no significant cluster formation was observed on Au surfaces. Accordingly, the average inter-cluster distance observed on -NH2 surfaces was relatively smaller (3.0 ±â€¯0.6 µm) as compared to that on other surfaces. Overall, these data suggest favorable initial biofilm growth on more hydrophilic and positively-charged surfaces. Furthermore, the analysis of the mean fluorescence intensity revealed preferred initial adhesion of key microbes (archaea) on -OH and -NH2 surfaces. Indeed, results obtained from this study would be beneficial in designing selective biointerfaces for certain biofilm carriers in a typical wastewater bioreactor. Importantly, our elastomeric flow cell integrated with SAM-modified surfaces demonstrated an ideal platform for high-throughput investigation of wastewater biofilm under controlled environments.

Enrichment and characterization of bacterial consortia for degrading 2-mercaptobenzothiazole in rubber industrial wastewater.

Benzothiazoles especially 2-mercaptobenzothiazole (2-MBT) in rubber industrial wastewater can be released into the environment. They can cause adverse health impacts. This study aimed to obtain efficient 2-MBT-degrading bacteria for wastewater application. The bacterial consortia were enriched by incubating rubber wastewater sludge in a medium containing 2-MBT for 28 days. Stepwise acclimatization was conducted with increasing 2-MBT concentrations from 50 to 200 mg L-1 in nitrogen-containing medium for 76 days. The process significantly increased the bacterial number and changed the dominant populations. Among these consortia, the EN consortium from benzothiazole-containing sludge had the highest specific 2-MBT biodegradation rate of 5.2 ± 0.5 mg L-1 day-1 mg protein-1 and could degrade up to 300 mg L-1 2-MBT. From 16S rRNA gene analysis, Pseudomonas was the dominant genus at approximately 70 % of the total population. Stenotrophomonas was the second most abundant populations and have never been reported for 2-MBT biodegradation. The EN consortium removed 65-79 % and 90-93 % of 112 mg L-1 2-MBT and ∼4000 mg L-1 COD in rubber wastewater, respectively, which were significantly higher than the values of natural attenuation. Therefore, the EN consortium could be an ideal inoculum for the post-treatment of benzothiazoles in rubber industrial wastewater.

Diverse Microbial Community Profiles of Propionate-Degrading Cultures Derived from Different Sludge Sources of Anaerobic Wastewater Treatment Plants.

Anaerobic digestion (AD) has been used for wastewater treatment and production of renewable energy or biogas. Propionate accumulation is one of the important problems leading to an unstable system and low methane production. Revealing propionate-degrading microbiome is necessary to gain a better knowledge for alleviation of the problem. Herein, we systematically investigated the propionate-degrading cultures enriched from various anaerobic sludge sources of agro-industrial wastewater treatment plants using 16S rRNA gene sequencing. Different microbial profiles were shown even though the methanogenic activities of all cultures were similar. Interestingly, non-classical propionate-degrading key players Smithella, Syntrophomonas, and Methanosaeta were observed as common prevalent taxa in our enriched cultures. Moreover, different hydrogenotrophic methanogens were found specifically to the different sludge sources. The enriched culture of high salinity sludge showed a distinct microbial profile compared to the others, containing mainly Thermovirga, Anaerolinaceae, Methanosaeta, Syntrophobactor, and Methanospirillum. Our microbiome analysis revealed different propionate-degrading community profiles via mainly the Smithella pathway and offers inside information for microbiome manipulation in AD systems to increase biogas production corresponding to their specific microbial communities.

Nylon fibers as supporting media in anaerobic hybrid reactors: it's effects on system's performance and microbial distribution.

The performances of three anaerobic hybrid reactors with various nylon fiber densities per packed bed volume (33, 22, and 11 kg/m(3) in R1, R2, and R3, respectively) as supporting media were evaluated through their ability to remove organic compounds in cassava starch wastewater. In addition, the distributions of non-methanogenic and methanogenic population in the reactors were investigated. During a 6-month operation, the organic loading rate was increased in stepwise from 0.5 to 4.0 kg COD/m3/day and the hydraulic retention time (HRT) shortened to 5.4 days. The COD removal efficiency was more favorable in R1 (87%) and R2 (84%) than in R3 (70%). The total biomass in the reactors with greater nylon fiber densities was also higher and increased from 20.4 to 67.3 g VSS and to 57.5 g VSS in R1 and R2, respectively. When the HRT was further shortened to 3 days, however, the efficiency of both reactors demonstrated a declining trend and reached 74% in R1 and 61% in R2. The distribution of microbial populations involved in the reactors was determined using the Most Probable Number technique. The result showed the lowest number of methanogens in R3 which correlated well to its relatively low efficiency. The number of non-methanogens in all reactors was, nonetheless, comparable. By shortening the HRT to 3 days, the methanogenic population in R2 diminished in both attached and suspended biomass whereas a slight reduction was detected only in the attached biomass of R1.