Iron deficiency and bioavailability in anaerobic batch and submerged membrane bioreactors (SAMBR) during organic shock loads

The impact of calcium supplementation on methane fermentation and ammonia inhibition of fish processing wastewater

The effect of trace metal supplementation on the methane fermentation of fish processing wastewater (FPW) was studied in both batch and continuous experiments using a self-agitated anaerobic baffled reactor (SA-ABR). In the batch experiments, a single supplementation of Ca²⁺, Co²⁺ and Fe²⁺ was show to have a significant positive impact on the performance of methane fermentation. The continuous experiment results showed that supplementation with 1.5 g-Ca²⁺/L-substrate remarkably enhanced the performance of methane fermentation of the SA-ABR in treating FPW with the optimal organic loading rate achieved at 7.62 g-COD/L/d. During the steady states (stages 2 to 5), the average removal efficiencies of COD, protein, carbohydrate and lipid were 89, 85, 80 and 91%, respectively. The biogas conversion rates were in the range of 0.39 to 0.45 L-biogas/g-COD with a high methane content of 74%. Besides, Ca²⁺ supplementation also improved the resistance of the methane fermentation system to ammonia inhibition.

Evaluation of the influence of trace metals on methane production from domestic sewage, using the Plackett-Burman experimental design

Methanogenesis involves several enzymes with trace metal components that catalyze major metabolic pathways and, therefore, requires a sufficient supply of micronutrients such as iron, nickel or cobalt. The statistically-based Plackett-Burman experimental design was adopted in this study to identify which trace metal have a statistically significant effect on the maximum methane production from domestic sewage. The addition of Barium (Ba), Cobalt (Co), Copper (Cu), Iron (Fe), Manganese (Mn), Nickel (Ni) and Selenium (Se) was tested in batch reactors using domestic sewage as the substrate and sewage sludge as the inoculum. The results showed that the addition of Fe was statistically significant, positively affecting the maximum CH₄ production (p-value 0.05). The results are expressed in L of CH₄ per g of Chemical Oxygen Demand added, increasing it from 0.10 to 0.13 LCH₄ gCOD_add^-1. In L of CH₄ per g of Volatile Solids, increased it from 0.031 to 0.040 LCH₄ gVS^-1. The addition of Se was statistically significant, but with a negative effect on the maximum methane production (p-value 0.002), which decreased from 0.13 to 0.10 LCH₄.gCOD_add^-1. Moreover, six different Fe concentrations (0, 40, 80, 120, 160 and 200 mgL^-1) were tested, showing that the addition of 120 mgL^-1 had the greatest effect for statistically improving the maximum methane production, with 33% improvement (0.12 ± 0.003 to 0.16 ± 0.012 LCH₄ gCOD_add^-1) compared to no addition of Fe and the specific CH₄ production to 0.040 ± 0.001 LCH₄ gVS^-1.

The effect of Fe2NiO4 and Fe4NiO4Zn magnetic nanoparticles on anaerobic digestion activity

Two types of magnetic nanoparticles (MNPs), i.e. Ni ferrite nanoparticles (Fe₂NiO₄) and Ni Zn ferrite nanoparticles (Fe₄NiO₄Zn) containing the trace metals Ni and Fe, were added to the anaerobic digestion of synthetic municipal wastewater at concentrations between 1 and 100 mg Ni L^-1 in order to compare their effects on biogas (methane) production and sludge activity. Using the production of methane over time as a measure, the assays revealed that anaerobic digestion was stimulated by the addition of 100 mg Ni L^-1 in Fe₂NiO₄ NPs, while it was inhibited by the addition of 1-100 mg Ni L^-1 in Fe₄NiO₄Zn NPs. Especially at 100 mg Ni L^-1, Fe₄NiO₄Zn NPs resulted in a total inhibition of anaerobic digestion. The metabolic activity of the anaerobic sludge was tested using the resazurin reduction assay, and the assay clearly revealed the negative effect of Fe₄NiO₄Zn NPs and the positive effect of Fe₂NiO₄ NPs. Re-feeding fresh synthetic medium reactivated the NPs added to the anaerobic sludge, except for the experiment with 100 mg Ni L^-1 addition of Fe₄NiO₄Zn NPs. The findings in this present study indicate a possible new strategy for NPs design to enhance anaerobic digestion.

ADM1 based mathematical model of trace element precipitation/dissolution in anaerobic digestion processes

Due to the complex biogeochemistry of trace elements (TEs, e.g. Fe, Ni and Co) in anaerobic digestion processes, their role and fate is poorly understood. Challenging, time consuming and low detection limits of analytical procedures necessitate recruitment of mathematical models. A dynamic mathematical model based on anaerobic digestion model no.1 (ADM1) has been proposed to simulate the effect of TEs. New chemical equilibrium association/dissociation and precipitation/dissolution reactions have been implemented to determine TE bioavailability and their effect on anaerobic digestion. The model considers interactions with inorganic carbonate (HCO₃^- and CO₃^2-), phosphate (PO₄^3-, HPO₄^2-, H₂PO₄^-) and sulfide (HS^- and S^2-). The effect of deficiency, activation, inhibition and toxicity of TEs on the biochemical processes has been modelled based on a dose-response type inhibition function. The new model can predict: the dynamics of TEs (among carbonate, sulfide and phosphate); the starvation of TEs; and the effect of initial sulfur-phosphorus ratio in an in-silico batch anaerobic system.

Post-treatment of anaerobic membrane bioreactor (AnMBR) effluent using activated carbon

Anaerobic membrane bioreactors (AnMBR) are very effective for wastewater treatment, however, with the antibiotic ciprofloxacin (CIP) (0-4.7 mg CIP/L) in the feed their performance decreases, the characteristics of the effluent changes, and further treatment is needed to recycle or discharge the treated effluent. Batch experiments using six activated carbons to treat AnMBR effluents resulting from the treatment of a synthetic wastewater containing ciprofloxacin were carried out at 35 °C. 22-82% COD was removed at a dose of 1 g activated carbon/L, while size characterization showed the 13.4 kDa and <1 kDa fractions were the most difficult to adsorb, while CIP was often removed with high efficiencies of mainly 100%. Significant removal of VFAs also occurred, up to 100%, and this contributed greatly to COD removal. Nitrogen containing compounds and phenols showed the highest removal (∼100%), whereas other groups such as esters, alkanes, and alkenes showed lower removal efficiency.

Mechanism on emulsified vegetable oil stimulating nitrobenzene degradation coupled with dissimilatory iron reduction in aquifer media

Microbial dissimilatory iron reduction could remediate reducible pollutants in groundwater, such as nitrobenzene (NB). But the natural attenuation rate in aquifer is limited. To stimulate this process, emulsified vegetable oil (EVO) was injected as a remediation agent. The mechanism of this process was studied. Results showed that the addition of EVO made iron easier used by microorganisms and thus promoted dissimilatory iron reduction. The readily used Fe(III) served as electron acceptor and was reduced to Fe(II). Fe(II) supplied electrons to NB, with NB reduced to aniline. Sulphide in the aquifer media also donated electrons and oxidized to polysulfide, then forming precipitates with Fe(II) to the surface of aquifer media, and thus slowing down the electron supplying of EVO and forming permanent efficiency for NB remediation. The work helps to complete a systematic understanding of NB remediation process under stimulation of EVO.

Effect of operating conditions on speciation and bioavailability of trace metals in submerged anaerobic membrane bioreactors

This study investigated the effect of changes in pH (7, 6.5 and 6), hydraulic retention time (HRT) (6h, 4h, and 2h), solids retention time (SRT) (100d and 25d) on the speciation of trace metals (TMs) in submerged anaerobic membrane bioreactors (SAMBRs). The results showed that the metal retention capacity of SAMBRs reduced when the pH, HRT and SRT were reduced i.e. up to 21.9%, 39.1%, and 17.1%, respectively, but it was also found that the speciation of these TMs generally shifted towards highly bioavailable fractions i.e. Soluble and Exchangeable. The degree of shifting in speciation depended on the affinity of the TMs for anaerobic sludge and their sensitivity to the changes. TMs with the most and the least significant changes in speciation were Fe and Mn, respectively.

Effects of trace metal deficiency and supplementation on a submerged anaerobic membrane bioreactor

This study examined the effects of a deficiency in trace metals (TMs) on the performance of a submerged anaerobic membrane bioreactor (SAMBR). When trace metals were excluded from the feed to the SAMBR, COD removal and methane yield reduced while VFAs in the effluent increased. A reduction of up to 37.48% in the total metal content in the reactor was observed, while the less bioavailable fractions increased up to 13.29%. Pulse addition of trace metals for 7 days at 5-times the daily metal loading was effective in improving the performance of the SAMBR by increasing the amount of trace metals in the bioavailable fractions from 2.12% to 11.92%, with up to 87.7% of added metals retained in the reactor within 24h. However, the second and third pulse at 5 and 10-times daily metal loading did not result in similar changes in metal speciation and might have inhibited the methanogens.

Fouling reduction using adsorbents/flocculants in a submerged anaerobic membrane bioreactor

Using adsorbents/flocculants in anaerobic membrane bioreactors (AnMBRs) to reduce membrane fouling is comparatively rare. This study evaluated 8 additives: 3 powdered activated carbons, 2 granular activated carbons, 1 cationic polymer, and 2 metal salts to identify the best additive and dose to minimise membrane fouling. Small cross flow filtration tests showed 400mg/L PAC SAE2, or 150mg/L FeCl₃, reduced the transmembrane pressure (TMP) rise from 0.94 to 0.06kPa/h, indicating excellent fouling reduction. The best filtration performance correlated with a significant reduction in supernatant supracolloidal particles, colloids and SMPs. FESEM-EDX showed that PAC SAE 2 and FeCl₃ reduced the thickness of the fouling layer dramatically, while FeCl₃ increased sludge floc size and particle size of the colloids, while decreasing the negative charge of colloids, and SMP size. Furthermore, Fe was not found in the supernatant or effluent, but precipitated with the solids, which is beneficial for its long-term use.

Effect of Ethylenediamine-N,N'-disuccinic acid (EDDS) on the speciation and bioavailability of Fe2+ in the presence of sulfide in anaerobic digestion

The effects of a biodegradable chelating agent, Ethylenediamine-N,N'-disuccinic acid (EDDS), on the speciation and bioavailability of iron (Fe²⁺) in anaerobic digestion were examined. Fe²⁺ supplementation at 10mg/L increased methane yield, but the presence of 8mg/L sulfide led to the precipitation of Fe²⁺ as FeS which limited its bioavailability. The results confirmed that the EDDS could replace common chelating agents with low biodegradability (EDTA and NTA), and improve the bioavailability of Fe²⁺ by forming an Fe-EDDS complex, thereby protecting Fe²⁺ from sulfide precipitation. Experimental findings from sequential extraction using the Community Bureau of Reference (BCR) method, and quantification of free EDDS and Fe-EDDS complex using UHPLC, confirmed that 29.82% of Fe²⁺ was present in bioavailable forms, i.e. soluble and exchangeable, when EDDS was added at 1:1 molar ratio to Fe²⁺. As a result, the methane production rate increased by 11.17%, and the methane yield increased by 13.25%.