Methylotrophic methanogenesis induced by ammonia nitrogen in an anaerobic digestion system.

OBJECTIVES: This lab-scale study aimed to investigate the effect of total ammonia nitrogen (TAN) stress on the methanogenic activity and the taxonomic and functional profiles of the microbial community of anaerobic sludge (AS) from a full-scale bioreactor. METHODS: The AS was subjected to a stepwise increase in TAN every 14 days at concentrations of 1, 2, 2.5, 3, 3.5, and 4 g TAN/L (Acclimated-AS or AAS). This acclimation stage was followed by an ammonia stress stage (4 g/L). A blank-AS (BAS) was maintained without TAN during the acclimation stage. In the second stress stage (ST), the BAS was divided into two new treatments: a control (BAS') and one that received a shock load of TAN of 4 g/L (SBAS'). Methane production was measured, and a metagenomic analysis was conducted to describe the microbial community. RESULTS: A decrease in the relative abundance of Methanothrix soehngenii of 16 % was related to a decrease of 23 % in the methanogenic capacity of AAS when comparing with the final stage of BAS. However, recovery was observed at 3.5 g TAN/L, and a shift to methylotrophic metabolism occurred, indicated by a 4-fold increase in abundance of Methanosarcina mazei. The functional analysis of sludge metagenomes indicated that no statistical differences (p > 0.05, RM ANOVA) were found in the relative abundance of methanogenic genes that initiate acetoclastic and hydrogenotrophic pathways (acetyl-CoA synthetase, ACSS; acetate kinase, ackA; phosphate acetyltransferase, pta; and formylmethanofuran dehydrogenase subunit A, fwdA) into the BAS and AAS during the acclimation phase. The same was observed between groups of genes associated with methanogenesis from methylated compounds. In contrast, statistical differences (p < 0.05, one-way ANOVA) in the relative abundance of these genes were recorded during ST. The functional profiles of the genes involved in acetoclastic, hydrogenotrophic, and methylotrophic methanogenic pathways were brought to light for acclimatation and stress experimental stages. CONCLUSIONS: TAN inhibited methanogenic activity and acetoclastic metabolism. The gradual acclimatization to TAN leads to metabolic and taxonomic changes that allow for the subsequent recovery of methanogenic functionality. The study highlights the importance of adequate management of anaerobic bioprocesses with high nitrogen loads to maintain the methanogenic functionality of the microbial community.

Toilet effluent separation and brown water treatment: Survey and initial feasibility testing in Mexico.

Separation of domestic effluents at the source and the utilization of low-flush toilets offer alternative approaches for developing efficient wastewater treatment systems while promoting energy generation through anaerobic digestion. This study focused on assessing toilet usage in Mexico and exploring the potential of anaerobic co-digestion of brown water (feces) and toilet paper as influential factors in wastewater treatment systems. A survey was conducted on a representative sample of Mexicans to gather information on toilet usage frequency, toilet paper use and disposal practices, as well as the type and quantity of commercial disinfectants and pharmaceutical compounds they use or consume. The survey revealed that per capita toilet paper consumption is 2.9 kg annually, that 58 % of respondents do not dispose used paper in the toilet, and that about 47 % use two to three cleaning and disinfection products. Notably, 97 % of the sampled Mexican population expressed a willingness to transition to more eco-friendly toilet options. Subsequently, in a second step, the anaerobic co-digestion of brown water with toilet paper was evaluated, demonstrating a relatively high production of volatile fatty acids but low methane production. This suggests an efficient hydrolysis/acidogenesis process coupled with restrained methanogenesis, probably due to pH decrease caused by acidogenesis. This study underscores that toilet paper and brown water are potential suitable substrates for anaerobic co-digestion. Furthermore, it sheds light on the behaviors of Mexican society regarding bathroom use and cleaning, contributing to the establishment of foundations for wastewater treatment systems with effluent separation at the source.

Start-up and performance of a downflow fluidised bed reactor for biological treatment of yellow wastewater and nutrient recovery.

The treatment of yellow water (human urine) in a downflow fluidised bed reactor (DFFBR) was investigated to evaluate biological ureolysis and nutrient recovery. The reactor was operated at 30±4 °C in batch mode, and reaction time = 1 d. The average immobilised biomass (as volatile solids, IVS) in the reactor was 2.5±0.9 g L-1support, and specific ureolytic activity was 121 g Urea-N g-1 IVS d-1. The kinetic parameters were 0.152 mol L-1 (Km) and 8 mol g-1 IVS d-1 (Vmax). The ureolysis efficiency was 93.4% and chemical oxygen demand removal efficiency was 31.2%, while total ammonium nitrogen (NH4+-N) production rate was 7 g L-1 d-1 and phosphate removal reached 26%. Precipitates recovery during biological treatment was 1.72±0.8 g. These results suggest that the treatment of yellow water in a DFFBR is a viable option for partial recovery of N and P.

Effect of organic loading rate on the performance of two-stage anaerobic digestion of the organic fraction of municipal solid waste (OFMSW).

Two-stage anaerobic digestion of the organic fraction of municipal solid waste (OFMSW) was carried out: hydrolysis and acidogenesis in a continuous anaerobic hydrolytic leach bed (AHLB) reactor loaded at different rates (Bv = 3.8-7 gVSSL⁻¹d⁻¹) and methanogenesis of leachates, diluted with municipal wastewater in an upflow anaerobic sludge blanket (UASB) reactor at organic loading rates of 6.6-13 gCODLr⁻¹d⁻¹. In the AHLB reactor, 51-76% and 58-71% volatile solids and chemical oxygen demand (COD) removal efficiencies were obtained. During the hydrolysis and acidogenesis phases, the effluents were at pH 4.93, the leachate had a volatile fatty acids concentration of 35 g/L and the biogas was composed only of CO2. The average methane production in the UASB in the load of 4.4 gVS L⁻¹ d⁻¹ in the AHLB was 3.32 LCH4Lr⁻¹d⁻¹ (yCH4 = 80%), with COD removal efficiency of 95% and methane yield 279 LCH4KgVS⁻¹OFMSW degraded.

High sulfate reduction efficiency in a UASB using an alternative source of sulfidogenic sludge derived from hydrothermal vent sediments.

Sulfidogenesis in reactors is mostly achieved through adaptation of predominantly methanogenic granular sludge to sulfidogenesis. In this work, an upflow anaerobic sludge blanket (UASB) reactor operated under sulfate-reducing conditions was inoculated with hydrothermal vent sediments to carry out sulfate reduction using volatile fatty acids (VFAs) as substrate and chemical oxygen demand (COD)/SO4 (-2) ratios between 0.49 and 0.64. After a short period of adaptation, a robust non-granular sludge was capable of achieving high sulfate reduction efficiencies while avoiding competence with methanogens and toxicity to the microorganisms due to high sulfide concentration. The highest sulfide concentration (2,552 mg/L) was obtained with acetate/butyrate, and sulfate reduction efficiencies were up to 98 %. A mixture of acetate/butyrate, which produced a higher yielding of HS(-), was preferred over acetate/propionate/butyrate since the consumption of COD was minimized during the process. Sludge was analyzed, and some of the microorganisms identified in the sludge belong to the genera Desulfobacterium, Marinobacter, and Clostridium. The tolerance of the sludge to sulfide may be attributed to the syntrophy among these microorganisms, some of which have been reported to tolerate high concentrations of sulfide. To the best of our knowledge, this is the first report on the analysis of the direct utilization of hydrothermal vent sediments as an alternate source of sludge for sulfate reduction under high sulfide concentrations.

Use of probiotics in aquaculture.

The growth of aquaculture as an industry has accelerated over the past decades; this has resulted in environmental damages and low productivity of various crops. The need for increased disease resistance, growth of aquatic organisms, and feed efficiency has brought about the use of probiotics in aquaculture practices. The first application of probiotics occurred in 1986, to test their ability to increase growth of hydrobionts (organisms that live in water). Later, probiotics were used to improve water quality and control of bacterial infections. Nowadays, there is documented evidence that probiotics can improve the digestibility of nutrients, increase tolerance to stress, and encourage reproduction. Currently, there are commercial probiotic products prepared from various bacterial species such as Bacillus sp., Lactobacillus sp., Enterococcus sp., Carnobacterium sp., and the yeast Saccharomyces cerevisiae among others, and their use is regulated by careful management recommendations. The present paper shows the current knowledge of the use of probiotics in aquaculture, its antecedents, and safety measures to be carried out and discusses the prospects for study in this field.

Methanization and mineralization of 2-chlorophenol by anaerobic digestion.

The aim of this study is to contribute to the knowledge about 2-Chlorophenol (2CP) mineralization and methanization in batch culture. This work was focused on evaluating the effect of: (i) the use of sludge with different periods of previous contact to 2CP, (ii) the electron donor addition in stoichiometric relation with 2CP and (iii) the presence of different initial oxygen concentrations. When compared with the control, 50 and 80 days of previous contact to 2CP resulted in a lag phase reduction of 57% and an increase in 2CP specific consumption rate (q(2CP)) of 114%. These results were obtained with no addition of an external electron donor. When acetate was used as an electron donor its consumption resulted independently of 2CP consumption. No lag phase and increase of 46% in q(2CP) was observed when phenol was used as an electron donor. In the third part when sludge without previous contact to 2CP was used, it was found that consumption efficiency (E(2CP)) and q(2CP) values did not increase in the presence of different oxygen concentrations. However, at the highest oxygen concentration, CH(4) yield (Y(CH(4))(-C/2CP-C)) and phenol yield (Y(phenol-C/2CP-C)) values decreased, while CO(2) yield value (Y(CO(2))(-C/2CP-C)) increased with regard to the methanogenic control. The use of sludge previously exposed to both 2CP and O(2) resulted in an increase in q(2CP) of 73%. However, among the different oxygen concentrations, no significant difference in E(2CP) or q(2CP) values was observed when compared to the control without oxygen. Therefore, previous contact to 2CP resulted in being a key factor for improving 2CP mineralization and methanization in batch culture.

Anaerobic biodegradability and inhibitory effects of some anionic and cationic surfactants.

The anaerobic biodegradability and inhibitory effects on the methane production of three different surfactants, two anionic: sodium lauryl sulfate (SLS) and sodium dodecylbenzene sulfonate (SDBS), and a cationic surfactant: trialkyl-methylammonium chloride (TMAC), were evaluated with two different anaerobic sludges, granular and flocculent. Five different concentrations of the surfactants, 5, 50, 100, 250 and 500 mg/L, were tested. SLS was biodegraded at concentrations of 5, 50 and 100 mg/L with flocculent sludge and at 100 and 250 mg/L with granular sludge. However an inhibitory effect on methane production was observed in both sludges at 500 mg/L. The results indicate that SDBS was not biodegradable under anoxic conditions. TMAC was slightly degraded 50 and 100 mg/L with the flocculent sludge, and from 100 to 500 mg/L with the granular sludge.

Efecto del oxígeno y la glucosa en la metanogénesis y mineralización de resinas poliméricas / The effect of oxygen and glucose on polymeric resin methanogenesis and mineralisation

The effect of dissolved oxygen concentration and glucose on polymeric resin compounds’ methanogenesisand mineralisation was examined in batch cultures. They were inoculated with sludge from an upflow anaerobicsludge blanket reactor fed with polymeric resin compounds and 1.0 mg L-1 steady-state dissolved oxygen.All tests were carried out with 1,500 mg L-1 chemical oxygen demand (COD), at 30±2ºC, with 23.8 g L-1 volatile suspended solids (VSS) as inoculum and 1:1 COD/VSS ratio. The effect of different dissolved oxygen concentrations showed that COD efficiently removed glucose whilst methanogenic activity remained constant at low concentrations (0.6 and 1.0 mg L-1), but polymeric resin compounds’ COD removal efficiency increased 58.1±1% whilst methane yield decreased, due to the higher aerobic mineralisation of carbon to carbon dioxide. The result of different glucose/polymeric resin compound ratios in the presence of 0.6 mg L-1 dissolved oxygen showed that glucose did not improve polymeric resin compound removal. However, methanogenic activity decreased by 75% with polymeric resin compounds as substrate compared to methanogenic activity with glucose as sole carbon source, suggesting that the presence of glucose promotes conditions for highertolerance to oxygen. The presence of low dissolved oxygen concentrations therefore promotes polymeric resin compounds’ methanogenesis and mineralisation.

En el presente trabajo se evaluó el efecto de la concentración de oxígeno disuelto (OD) y la presencia de laglucosa en la metanogénesis y mineralización de los compuestos de resinas poliméricas, mediante cultivos en lote. El inóculo utilizado para los cultivos fueron lodos procedentes de un reactor de lecho de lodos con flujoascendente UASB (por sus siglas en inglés), alimentado con glucosa y aguas residuales de resinas poliméricas,y 1,0 mg L-1 d-1 de oxígeno disuelto en estado estacionario. Todas las pruebas fueron realizadas con 1500 mgL-1 de demanda química de oxígeno, a 30±2° C, con 23,8 g L-1 de sólidos suspendidos volátiles como inóculoy una relación demanda química de oxígeno / sólidos suspendidos volátiles de 1. El efecto de diferentesconcentraciones de oxígeno disuelto mostró que, para la glucosa, con bajas concentraciones (0,6 y 1,0 mgL-1) la eficiencia de remoción de la demanda química de oxígeno y la actividad metanogénicas permanecieronconstantes, pero la eficiencia de remoción de la demanda química de oxígeno para los compuestos de resinaspoliméricas aumentó 58,1±1% y el rendimiento de metano disminuyó, debido a que una mayor fracción delcarbono alimentado fue mineralizada a dióxido de carbono, posiblemente por una ruta aerobia. Los resultadoscon diferentes proporciones de glucosa / compuestos de resinas poliméricas (CRP) en presencia de 0,6 mg L-1 de oxígeno disuelto mostraron que la presencia de glucosa no mejoró la eliminación de los compuestosde resinas poliméricas. Sin embargo, la actividad metanogénica disminuyó en un 75% cuando solamente se usó a los compuestos de resinas poliméricas como sustrato, al compararla con la actividad metanogénica con glucosa como única fuente de carbono, sugiriendo que la glucosa no favorece la eliminación de los compuestosde resinas poliméricas, pero proporciona una mejor tolerancia al oxígeno..