Anaerobic Treatment Of Low-strength Wastewater Research Articles

Anaerobic treatment of low-strength municipal wastewater with electroactive magnetite-embedded granules under mainstream conditions

This study examined the potential for the anaerobic treatment of low-strength wastewater (250 mg chemical oxygen demand/L) using expanded granular sludge bed (EGSB) with conductive magnetite-embedded granules (MEGs) under mainstream conditions (25°C). The inclusion of magnetite, with high specific gravity and conductivity, enhanced the settleability, structural stability, and electron transfer capability of MEGs compared to granules without it. Within the hydraulic retention time (HRT) range of 4–12 h, the MEG-EGSB reactors maintained superior treatment performance, along with comparable or higher methane production, compared to the control EGSB reactors lacking MEGs. This performance enhancement was more pronounced under conditions of higher hydraulic and organic loading. The MEG-EGSB reactors achieved approximately 90% organic removal efficiency at 8–12-h HRTs, a range comparable to that of the aerobic activated sludge process, with minimal loss of magnetite. The results from RNA-based microbial community analysis, alone with the consistently higher methane content in the biogas from MEG-EGSB reactors, supported the potential development of electric syntrophy between exoelectrogenic bacteria and electrotrophic methanogens in electroactive MEGs. This capability of MEGs to promote electro-syntrophic methanogenesis could potentially enhance methanogenic degradation of organic matter. The overall findings suggest that the MEG-EGSB process is a promising candidate for anaerobic municipal wastewater treatment.

Specific affinity and relative abundance of methanogens in acclimated anaerobic sludge treating low-strength wastewater.

Kinetic parameters affecting effluent water quality including half saturation constant (Ks), maximum specific growth rate (μmax), and specific affinity ([Formula: see text], defined as μmax/Ks) were investigated using three types of anaerobic sludge (raw anaerobic digestion sludge referred to as unacclimated sludge, unacclimated sludge after endogenous decay, and sludge acclimated to low-strength wastewater in an anaerobic membrane bioreactor (AnMBR) for 360 days). Long-term acclimation to low-strength wastewater resulted in sludge with high specific affinity (1.6 × 10-3 L/mg COD/day for acclimated sludge compared to 4.1 × 10-4 L/mg COD/day for unacclimated sludge). The μmax values for unacclimated sludge and acclimated sludge were 0.08 and 0.07 day-1, respectively. The Ks values for unacclimated sludge and acclimated sludge were 194 ± 81 mg COD/L and 45 ± 13 mg COD/L, respectively. Although the Ks of unacclimated sludge after endogenous decay increased to 772 ± 74 mg COD/L, μmax increased to 0.35 day-1 as well, resulting in no statistically significant difference of [Formula: see text] between the two types of unacclimated sludge. Overall, [Formula: see text] is a better indicator than μmax or Ks alone for determining effluent water quality, as effluent substrate concentration is approximately inversely proportional to the specific affinity. 16S rRNA sequencing data analysis indicated a high abundance (85.8% of total archaea) of Methanosaeta in the microbial community after long-term acclimation. High [Formula: see text] associated with the enrichment of Methanosaeta appears to ensure successful anaerobic treatment of low-strength wastewater.

Anaerobic treatment of low-strength wastewater: A comparison between single and staged anaerobic fluidized bed membrane bioreactors

Performance of a single anaerobic fluidized membrane bioreactor (AFMBR) was compared with that of a staged anaerobic fluidized membrane bioreactor system (SAF-MBR) that consisted of an anaerobic fluidized bed bioreactor (AFBR) followed by an AFMBR. Both systems were fed with an equal COD mixture (200mg/L) of acetate and propionate at 25°C. COD removals of 93–96% were obtained by both systems, independent of the hydraulic retention times (HRT) of 2–4h. Over more than 200d of continuous operation, trans-membrane pressure (TMP) in both systems was less than 0.2bar without significant membrane fouling as a result of the scouring of membrane surfaces by the moving granular activated carbon particles. Results of bulk liquid suspended solids, extracellular polymeric substances (EPS), and soluble microbial products (SMP) analyses also revealed no significant differences between the two systems, indicating the single AFMBR is an effective alternative to the SAF-MBR system.

Low-temperature anaerobic treatment of low-strength pentachlorophenol-bearing wastewater

The anaerobic treatment of low-strength wastewater bearing pentachlorophenol (PCP) at psychro-mesophilic temperatures has been investigated in an expanded granular sludge bed reactor. Using an upward flow rate of 4 m h(-1), a complete removal of PCP, as well as COD removal and methanization efficiencies higher than 75% and 50%, respectively, were achieved. Methanogenesis and COD consumption were slightly affected by changes in loading rate, temperature (17-28°C) and inlet concentrations of urea and oils. Pentachlorophenol caused an irreversible inhibitory effect over both acetoclastic and hydrogenotrophic methanogens, being the later more resistant to the toxic effect of pentachlorophenol. An auto-inhibition phenomenon was observed at PCP concentrations higher than 10 mg L(-1), which was accurately predicted by a Haldane-like model. The inhibitory effect of PCP over the COD consumption and methane production was modelled by modified pseudo-Monod and Roediger models, respectively.

Microbial community structure and population dynamics of granules developed in expanded granular sludge bed (EGSB) reactors for the anaerobic treatment of low-strength wastewater at low temperature

The anaerobic biological treatment of sucrose-based, low-strength wastewater was investigated in expanded granular sludge bed (EGSB) reactors at low temperatures over a 300-day trial period. During the trial, the operating temperature was lowered in a stepwise manner from 20°C to 5°C. As a result, the reactors exhibited sufficient performances until 10°C operation. The COD removal rate was 3.1–3.8 kgCOD m− 3 day− 1 at 10°C. In particular, the COD removal rate increased gradually through the low-temperature operation; indeed, the later stages of the 10°C operation attained a rate similar to those achieved at 20°C and 15°C. This finding is especially practical for applications of psychrophilic methane fermentation. Additionally, the structure of the microbial community in the granular sludge was analyzed by clone analysis based on 16S rRNA genes and fluorescence in situ hybridization (FISH). As a result, the percentage of the phylum Firmicutes, which were assumed to be Anaerobivrio sp. and Lactococcus sp., greatly increased from 0.7% to 8.0% of the total cells, especially in the surface layer of the granular sludge. These bacteria would contribute to the degradation of the sucrose substrate anaerobically at ambient temperatures. Moreover, the results suggest that a Methanospirillum species, which is a H2-utilizing methanogen, increased from 0.5% to 6.7% during the low-temperature incubation, with a significant increase of methanogenic activity from H2/CO2 at 20°C. Thus, the Methanospirillum species detected in this study may have a key role as hydrogen scavenger during hydrogen-metabolism in low-temperature conditions.

Anaerobic treatment of low-strength wastewater with a high fraction of particulate matter in an unconventional two-phase ASBRs system

The results of a two-phase anaerobic system using anaerobic sequencing batch reactors (ASBRs), treating low-strength wastewater (COD ∼ 500 mg/L) with a high fraction of particulate organic matter (70%, COD basis), are presented. Two reactors in series were used; the first one was hydrolytic–acidogenic, while the second one was methanogenic. This configuration was proposed to promote high efficiency solids removal. During the experiment, 69% and 50% efficiencies of total COD removal were obtained for OLRs of 0.63 and 1.22 kgCOD/(m3 d), respectively. Values of the solubilized organic fraction (SOF) achieved in the hydrolytic–acidogenic reactor were within the range of 0.3–0.6 gCODsolubilized/gpCODremoved, and the average acidified organic fraction (AOF) was 0.6 gCODVFA-produced/gsCODfed. The methanogenic reactor had a VFA removal fraction (VFARF) between 0.4 and 0.6 gCODVFA-removed/gCODVFA-fed for the OLR of 0.63 and 1.22. The two-phase ASBR system is suitable, and can be implemented, for the anaerobic treatment of this kind of wastewater.

A simplified analysis of granule behavior in ASBR and UASB reactors treating low-strength synthetic wastewater

This work presents an analysis of the changes observed in granule characteristics of sludge in the treatment of synthetic wastewater at a concentration of about 500 mgCOD/L in batch, fed-batch (ASBR) and continuous (UASB) bench-scale reactors under similar experimental conditions. Physical and microbiological properties of the granules were characterized as average particle size and sedimentation time and by optical and epifluorescence microscopy. Several samples were analyzed in order to identify the morphologies. Granules from sequencing batch and fed-batch reactors, either with or without mechanical mixing, did not undergo any physical or microbiological changes. However, during the experiment granules from the UASB reactor agglomerated due to the formation and accumulation of a viscous material, probably of microbial origin, when operated at low superficial velocities (0.072, 0.10 and 0.19 m/h). When the superficial velocity was increased to 8.0-10.0 m/h by means of liquid-phase recirculation, the granules from the UASB reactor underwent flocculation and the microbiological characteristics changed in such a way that the equilibrium of microbial diversity in the inoculum was not maintained. As a result, the only reactor that maintained efficiency and good solids retention during the assays was the ASBR, showing that there is a correlation between maintenance of microbial diversity and operating mode in the case of anaerobic treatment of low-strength wastewaters.

Anaerobic Treatment of Low-Strength Wastewater in a Biofilm Reactor

A 3.9-L (70-cm high) upflow anaerobic filter (AF) packed with corrugated plastic rings was employed to evaluate the direct treatment of low-strength wastewater over a long period of operation (32 months at 25.4°C and 2 months at 15.5°C). The AF was fed four complex synthetic-type wastewaters with a low-solids content [chemical oxygen demand (COD) 325–403 mg L−1 soluble COD (SCOD) 86–339 mg L−1 and total suspended solids (TSS) 65–156 mg L−1] at organic loading rates (OLR) ranging from 0.02 to 0.91 kg COD m−3 d−1. Operation with filtered municipal wastewater supplemented with a sugar-nutrient based substrate (OLR 0.27–0.91 kg COD m−3 d−1) yielded removal efficiencies in the range of 72–80% for COD and 80–92% for TSS, and use of a completely synthetic substrate resulted in improved effluent quality. Under these test conditions, removal of organic matter and solids occurred within the first 40 cm of column height and accumulation within the reactor was not substantial or affected by the length of operation.

Feasibility of expanded granular sludge bed reactors for the anaerobic treatment of low‐strength soluble wastewaters

The application of the expanded granular sludge bed (EGSB) reactor for the anaerobic treatment of low-strength soluble wastewaters using ethanol as a model substrate was investigated in laboratory-scale reactors at 30oC. Chemical oxygen demand (COD) removal efficiency was above 80% at organic loading rates up to12 g COD/L . d with influent concentrations as low as 100 to 200 mg COD/L. These results demonstrate the suitability of the EGBS reactor for the anaerobic treatment of low-strength wastewaters. The high treatment performance can be attributed to the intense mixing regime obtained by high hydraulic and organic loads. Good mixing of the bulk liquid phase for the substrate-biomass contact and adequate expansion of the substrate-biomass contact and adequate expansion of the sludge bed for the degassing were obtained when the liquid upflow velocity (V(up)) was greater than 2.5 m/h. Under such conditions, an extremely low apparent K(s) value for acetoclastic methanogenesis of 9.8 mg COD/L was observed. The presence of dissolved oxygen in the wastewater had no detrimental effect on the treatment performance. Sludge piston flotation from pockets of biogas accumulating under the sludge bed occurred at V(up) lower than 2.5 m/h due to poor bed expansion. This problem is expected only in small diameter laboratory-scale reactors. A. more important restriction of the EGSB reactor was the sludge washout occurring at V(up) higher than 5.5 m/h and which was intensified at organic loads higher than 7 g COD/L. d due to buoyancy forces from the gas production. To achieve an equilibrium between the mixing intensity and the sludge hold-up, the operation should be limited to an organic loading rate of 7 g COD/L d. and to a liquid up-flow velocity between 2.5 and 5.5 m/h (c) 1994 John Wiley & Sons, Inc.