Stefano Papirio

Acid Mine Drainage Treatment in Fluidized-Bed Bioreactors by Sulfate-Reducing Bacteria: A Critical Review

Acid mine drainage is an important environmental problem related to the release of acidic, sulfate-, and metal-containing wastewater into the environment. Sulfate-reducing bacteria can be used for treating mining wastewaters and recovering metals in several bioreactor configurations. The fluidized-bed configuration is an efficient way for acid mine drainage remediation due to the high biomass retention, the great resistance to inhibitors, and the possibility to use high organic, sulfate, and metal loading rates at low hydraulic retention times. Additional research is needed to assess the removal of the organic rest-pollution and the factors that promote a better metal recovery in single-stage processes.

Biological inverse fluidized-bed reactors for the treatment of low pH- and sulphate-containing wastewaters under different COD conditions

The feasibility of removing sulphate using low-density polypropylene pellets as carrier material in two lactate-fed sulphidogenic inverse fluidized-bed reactors was investigated. Two different COD/sulphate ratios and two different feed–sulphate concentrations were used for the operation of the reactors. During the 242 days of operation, the robustness of the system was studied by suddenly decreasing the feed pH to 3.00. A 10% fluidization degree was used since the carrier material adopted showed not to be adequate to attain a satisfactory immobilization of the biomass with higher fluidization degrees. This resulted in a failure of the process when the feed pH was intentionally decreased to 3.00 in reactor 2, operated with a COD/sulphate ratio of 4.00. On the contrary, when a slightly acidic feed solution was fed to reactor 2, a 97% sulphate reduction efficiency was obtained. In reactor 1, operated with a COD/sulphate ratio of 0.67 throughout the experiment, COD removal and sulphate reduction efficiencies reached the highest values of 75% and 35%, respectively. Higher efficiencies were not achieved also due to the accumulation of acetate and the most likely presence of microbial competition between sulphate reducers and other microorganisms.

Trace elements dosing and alkaline pretreatment in the anaerobic digestion of rice straw

The effect of trace elements (TEs) addition and NaOH pretreatment on the anaerobic digestion of rice straw was investigated in batch tests. Co, Ni and Se were added to the raw rice straw at different dosages. The NaOH pretreatment was applied to the rice straw both alone and in combination with the addition of TEs, in order to evaluate potential synergistic effects of the pretreatment and the TEs supplementation on the biogas production yields. The results obtained showed that the alkaline pretreatment was more effective than the TEs addition in increasing the cumulative biogas production, causing a 21.4% enhancement of the final biomethane yield, whereas the increase due to TEs dosing was not statistically significant. The analysis of volatile fatty acids (VFAs) confirmed that the NaOH pretreatment resulted in a higher production of VFAs, indicating an increased hydrolysis, while TEs addition did not cause significant changes in the VFA concentrations.

Heavy Metal Removal from Wastewaters by Biosorption: Mechanisms and Modeling

Many industrial activities result in heavy metal dispersion in the environment worldwide. Heavy metals are persistent contaminants, which get into contact with living organisms and humans creating serious environmental disorders. Metals are commonly removed from wastewaters by means of physical-chemical processes, but often microbes are also enrolled to control metal fate. When microorganisms are used as biosorbents for metal entrapment, a process called “biosorption” occurs. Biosorption efficiency is significantly influenced by many parameters such as environmental factors, the sorbing material and the metal species to be removed, and highly depends on whether microbial cultures are alive or dead. Moreover, the presence of biofilm agglomerates is of major importance for metal uptake onto extracellular polymeric substances. In this chapter, the effect of the above mentioned variables on biosorption performance was reviewed. Among the environmental factors, pH rules metal mobility and speciation. Temperature has a lower influence with an optimal value ranging between 20 and 35 °C. The co-presence of more metals usually decreases the biosorption efficiency of each single metal. Biosorption efficiency can be enhanced by using living microorganisms due to the interaction with active functional groups and the occurrence of transport phenomena into the cells. The existing mathematical modeling approaches used for heavy metal biosorption were overviewed. Several isotherms, obtained in batch conditions, are available for modeling biosorption equilibria and kinetics. In continuous systems, most of the models are used to predict the breakthrough curves. However, the modeling of complex continuous-flow reactors requires further research efforts for better incorporating the effect of the operating parameters and hydrodynamics.

Elemental sulfur-based autotrophic denitrification and denitritation: microbially catalyzed sulfur hydrolysis and nitrogen conversions

The hydrolysis of elemental sulfur (S0) coupled to S0-based denitrification and denitritation was investigated in batch bioassays by microbiological and modeling approaches. In the denitrification experiments, the highest obtained NO3--N removal rate was 20.9 mg/l·d. In the experiments with the biomass enriched on NO2-, a NO2--N removal rate of 10.7 mg/l·d was achieved even at a NO2--N concentration as high as 240 mg/l. The Helicobacteraceae family was only observed in the biofilm attached onto the chemically-synthesized S0 particles with a relative abundance up to 37.1%, suggesting it was the hydrolytic biomass capable of S0 solubilization in the novel surface-based model. S0-driven denitrification was modeled as a two-step process in order to explicitly account for the sequential reduction of NO3- to NO2- and then to N2 by denitrifying bacteria.

Dewaterability of CAS and MBR Sludge: Effect of Biological Stability and EPS Composition

AbstractThe dewaterability of sludge from two conventional activated sludge (CAS) and three membrane bioreactor (MBR)–based wastewater treatment plants is investigated prior to and after anaerobic ...

Sensitivity analysis for an elemental sulfur-based two-step denitrification model

A local sensitivity analysis was performed for a chemically synthesized elemental sulfur (S0)-based two-step denitrification model, accounting for nitrite (NO2-) accumulation, biomass growth and S0 hydrolysis. The sensitivity analysis was aimed at verifying the model stability, understanding the model structure and individuating the model parameters to be further optimized. The mass specific area of the sulfur particles (a*) and hydrolysis kinetic constant (k1) were identified as the dominant parameters on the model outputs, i.e. nitrate (NO3-), NO2- and sulfate (SO42-) concentrations, confirming that the microbially catalyzed S0 hydrolysis is the rate-limiting step during S0-driven denitrification. Additionally, the maximum growth rates of the denitrifying biomass on NO3- and NO2- were detected as the most sensitive kinetic parameters.

Semi-continuous mono-digestion of OFMSW and Co-digestion of OFMSW with beech sawdust: Assessment of the maximum operational total solid content

In this study, mono-digestion of the organic fraction of municipal solid waste (OFMSW) and co-digestion of OFMSW with beech sawdust, simulating green waste, were used to investigate the maximum operational total solid (TS) content in semi-continuous high-solids anaerobic digestion (HS-AD). To alleviate substrate overloading in HS-AD, the effluent mass was relatively reduced compared to the influent mass, extending the mass retention time. To this aim, the reactor mass was daily evaluated, permitting to assess the reactor content removal by biogas production. During mono-digestion of OFMSW, the NH3 inhibition and the rapid TS removal prevented to maintain HS-AD conditions (i.e. TS ≥ 10%), without exacerbating the risk of reactor acidification. In contrast, the inclusion of sawdust in OFMSW permitted to operate HS-AD up to 30% TS, before acidification occurred. Therefore, including a lignocellulosic substrate in OFMSW can prevent acidification and stabilize HS-AD at very high TS contents (i.e. 20-30%).

Biokinetics of microbial consortia using biogenic sulfur as a novel electron donor for sustainable denitrification

In this study, the biokinetics of autotrophic denitrification with biogenic S0 (ADBIOS) for the treatment of nitrogen pollution in wastewaters were investigated. The used biogenic S0, a by-product of gas desulfurization, was an elemental microcrystalline orthorhombic sulfur with a median size of 4.69 µm and a specific surface area of 3.38 m2/g, which made S0 particularly reactive and bioavailable. During denitritation, the biomass enriched on nitrite (NO2-) was capable of degrading up to 240 mg/l NO2--N with a denitritation activity of 339.5 mg NO2--N/g VSS·d. The use of biogenic S0 induced a low NO2--N accumulation, hindering the NO2--N negative impact on the denitrifying consortia and resulting in a specific denitrification activity of 223.0 mg NO3--N/g VSS·d. Besides Thiobacillus being the most abundant genus, Moheibacter and Thermomonas were predominantly selected for denitrification and denitritation, respectively.