Pamela J. Welz

Microbial community structure stability, a key parameter in monitoring the development of constructed wetland mesocosms during start-up

Constructed wetlands (CWs) are known to be effective for treating waste streams, and pilot-scale CWs are useful for assessing the impact of pollutants and their remediation. However, little is known with respect to the establishment of these mesocosm systems or the parameters which should be monitored in assessing system equilibration, i.e. when they present stabilised physical and biological patterns. The aim of this study was to evaluate the temporal aspects of CW equilibration as a basis for future studies of system response to amendment. Microbial biomass and hydraulic conductivity values were monitored and microbial community fingerprints were obtained using denaturing gradient gel electrophoresis (DGGE). This study showed that microbial community fingerprinting provides a valuable tool for assessing the time scales of equilibration, as it was the last parameter which stabilised during the equilibration period. Hydraulic conductivity was also an important parameter in determining the time scale for initiation of the equilibration process during the study. For a CW of the dimensions used (173 cm long/106 cm large/30 cm depth), community equilibration times demonstrated on the basis of similar microbial community structures were found to be on the order of 100 days.

Phenolic removal processes in biological sand filters, sand columns and microcosms

This study evaluated the removal processes involved in the removal of the phenolic component of winery wastewater in biological sand filters, sand columns and sand microcosms. It was found that at low influent phenolic concentrations, complete organic removal was accomplished, but at high concentrations, there was incomplete substrate removal and an accumulation of potentially toxic metabolites, including catechol. The sand provided a suitable substrate for the treatment of phenolic-laden waste, and both biotic (48%) and abiotic (52%) removal mechanisms effected the removal of model phenolics. Prior acclimation of microbial communities increased the biodegradation rate of phenolic acids significantly.

Assessment of temporal and spatial evolution of bacterial communities in a biological sand filter mesocosm treating winery wastewater

To assess the impact of winery wastewater (WW) on biological sand filter (BSF) bacterial community structures, and to evaluate whether BSFs can constitute alternative and valuable treatment‐ processes to remediate WW.

Treatment of high ethanol concentration wastewater by biological sand filters : Enhanced COD removal and bacterial community dynamics

Winery wastewater is characterized by its high chemical oxygen demand (COD), seasonal occurrence and variable composition, including periodic high ethanol concentrations. In addition, winery wastewater may contain insufficient inorganic nutrients for optimal biodegradation of organic constituents. Two pilot-scale biological sand filters (BSFs) were used to treat artificial wastewater: the first was amended with ethanol and the second with ethanol, inorganic nitrogen (N) and phosphorus (P). A number of biochemical parameters involved in the removal of pollutants through BSF systems were monitored, including effluent chemistry and bacterial community structures. The nutrient supplemented BSF showed efficient COD, N and P removal. Comparison of the COD removal efficiencies of the two BSFs showed that N and P addition enhanced COD removal efficiency by up to 16%. Molecular fingerprinting of BSF sediment samples using denaturing gradient gel electrophoresis (DGGE) showed that amendment with high concentrations of ethanol destabilized the microbial community structure, but that nutrient supplementation countered this effect.

Minor differences in sand physicochemistry lead to major differences in bacterial community structure and function after exposure to synthetic acid mine drainage

The formation of environmentally toxic acidic waste from mining activities is a world-wide problem. Neutralization of this waste can be accomplished by physicochemical and/or biological means. In this short-term study, synthetic acid mine drainage was added to sand-filled mesocosms containing silica-dominated (quartz) sand. Glucose was added as a carbon source for microbial iron and/or sulphate reduction. Replicates contained two separate batches of sand obtained from the same quarry site. The investigations used to assess and compare the chemical and biological functioning of the replicates included system hydraulic conductivity measurements, sand chemistry, effluent chemistry and bacterial community fingerprinting. Minor differences in composition of the sand, including the levels of available nutrients and micronutrients, resulted in major differences in measured parameters. Significant differences in effluent chemistry were found in systems containing different batches of sand. It was demonstrated that the characteristics of the sand and the presence of acid mine drainage (AMD) impacted the bacterial community structure and function. The importance of the physical substrate on the selection of functional microbial communities in systems remediating AMD should not be under-estimated. The physical substrate should be carefully selected and it may be prudent to include small-scale comparative studies in each particular setting prior to full-scale implementation.

Selection of Clostridium spp. in biological sand filters neutralizing synthetic acid mine drainage

In this study, three biological sand filter (BSF) were contaminated with a synthetic iron- [1500 mg L⁻¹ Fe(II), 500 mg L⁻¹ Fe(III)] and sulphate-rich (6000 mg L⁻¹ SO₄²⁻) acid mine drainage (AMD) (pH = 2), for 24 days, to assess the remediation capacity and the evolution of autochthonous bacterial communities (monitored by T-RFLP and 16S rRNA gene clone libraries). To stimulate BSF bioremediation involving sulphate-reducing bacteria, a readily degradable carbon source (glucose, 8000 mg L⁻¹) was incorporated into the influent AMD. Complete neutralization and average removal efficiencies of 81.5 (±5.6)%, 95.8 (±1.2)% and 32.8 (±14.0)% for Fe(II), Fe(III) and sulphate were observed, respectively. Our results suggest that microbial iron reduction and sulphate reduction associated with iron precipitation were the main processes contributing to AMD neutralization. The effect of AMD on BSF sediment bacterial communities was highly reproducible. There was a decrease in diversity, and notably a single dominant operational taxonomic unit (OTU), closely related to Clostridium beijerinckii, which represented up to 65% of the total community at the end of the study period.

The effect of biogenic and chemically manufactured silver nanoparticles on the benthic bacterial communities in river sediments

This study was conducted to determine and compare the effect of chemically-synthesised and biogenic silver nanoparticles on the benthic bacterial community structure in mesocosms containing sediment from three rivers in geographical sites with different population densities (low, medium, high), and therefore likely to be associated with respective low, moderate and high degrees of anthropogenic input. The nanoparticles were applied at the upper limit expected to accumulate in impacted environments (4 μg kgsed-1). The biomass, concentrations of elements, including selection metals (P, K, Na, K, Ca, Mg, Zn, Cu, Al, Ag) were all significantly higher at the high density than at the low density sites. Bacterial community profiling (terminal restriction fragment length polymorphism and amplicon sequencing) showed that the bacterial community structure in the sediments from the high population density site were resilient to environmental perturbations [adjustment from in-situ to ex-situ (laboratory) conditions], as well as to exposure to silver nanoparticles, with the converse being true for the low population density site. Results obtained from amplicon sequencing were interrogated to the lowest taxonomic level with a relative abundance >5%. Proteobacteria was the most abundant phylum in all the sediments. Notable resistance (increased relative abundance) to one or both forms of silver nanoparticles was seen in the class Thermoleophilia, and the orders Myxococcales, Bacteriodales, Pirellules CCU21 and iii 1-15 (class Acidobacteria 6). Conversely, sensitivity was demonstrated in the family Koribacteraceae and the orders Rhizobiales, Ellin 329 and Gemmatales. It is recommended that pro-active environmental monitoring is performed in aquatic systems receiving point source pollution from wastewater treatment plants in order to assess the accumulation of silver nanoparticles. If necessary, measures should be implemented to mitigate the entry of silver nanoparticles, especially into more vulnerable environments.