Christian Nyrop Albers

Is biological treatment a viable alternative for micropollutant removal in drinking water treatment processes

In western societies, clean and safe drinking water is often taken for granted, but there are threats to drinking water resources that should not be underestimated. Contamination of drinking water sources by anthropogenic chemicals is one threat that is particularly widespread in industrialized nations. Recently, a significant amount of attention has been given to the occurrence of micropollutants in the urban water cycle. Micropollutants are bioactive and/or persistent chemicals originating from diverse sources that are frequently detected in water resources in the pg/L to μg/L range. The aim of this review is to critically evaluate the viability of biological treatment processes as a means to remove micropollutants from drinking water resources. We first place the micropollutant problem in context by providing a comprehensive summary of the reported occurrence of micropollutants in raw water used directly for drinking water production and in finished drinking water. We then present a critical discussion on conventional and advanced drinking water treatment processes and their contribution to micropollutant removal. Finally, we propose biological treatment and bioaugmentation as a potential targeted, cost-effective, and sustainable alternative to existing processes while critically examining the technical limitations and scientific challenges that need to be addressed prior to implementation. This review will serve as a valuable source of data and literature for water utilities, water researchers, policy makers, and environmental consultants. Meanwhile this review will open the door to meaningful discussion on the feasibility and application of biological treatment and bioaugmentation in drinking water treatment processes to protect the public from exposure to micropollutants.

Rapid Mineralization of the Phenylurea Herbicide Diuron by Variovorax sp. Strain SRS16 in Pure Culture and within a Two-Member Consortium

ABSTRACT The phenylurea herbicide diuron [N-(3,4-dichlorophenyl)-N,N-dimethylurea] is widely used in a broad range of herbicide formulations, and consequently, it is frequently detected as a major water contaminant in areas where there is extensive use. We constructed a linuron [N-(3,4-dichlorophenyl)-N-methoxy-N-methylurea]- and diuron-mineralizing two-member consortium by combining the cooperative degradation capacities of the diuron-degrading organism Arthrobacter globiformis strain D47 and the linuron-mineralizing organism Variovorax sp. strain SRS16. Neither of the strains mineralized diuron alone in a mineral medium, but combined, the two strains mineralized 31 to 62% of the added [ring-U-14C]diuron to 14CO2, depending on the initial diuron concentration and the cultivation conditions. The constructed consortium was used to initiate the degradation and mineralization of diuron in soil without natural attenuation potential. This approach led to the unexpected finding that Variovorax sp. strain SRS16 was able to mineralize diuron in a pure culture when it was supplemented with appropriate growth substrates, making this strain the first known bacterium capable of mineralizing diuron and representatives of both the N,N-dimethyl- and N-methoxy-N-methyl-substituted phenylurea herbicides. The ability of the coculture to mineralize microgram-per-liter levels of diuron was compared to the ability of strain SRS16 alone, which revealed the greater extent of mineralization by the two-member consortium (31 to 33% of the added [ring-U-14C]diuron was mineralized to 14CO2 when 15.5 to 38.9 μg liter−1 diuron was used). These results suggest that the consortium consisting of strains SRS16 and D47 could be a promising candidate for remediation of soil and water contaminated with diuron and linuron and their shared metabolite 3,4-dichloroaniline.

Fungal–bacterial consortia increase diuron degradation in water-unsaturated systems

Bioremediation of pesticide-polluted soil may be more efficient using mixed fungal-bacterial cultures rather than the individual strains alone. This may be due to cooperative catabolism, where the first organism transforms the pollutant to products which are then used by the second organism. In addition, fungal hyphae may function as transport vectors for bacteria, thereby facilitating a more effective spreading of degrader organisms in the soil. A more rapid mineralization of the phenylurea herbicide diuron was found in sand with added microbial consortia consisting of both degrading bacteria and fungi. Facilitated transport of bacteria by fungal hyphae was demonstrated using a system where herbicide-spiked sand was separated from the consortium by a layer of sterile glass beads. Several fungal-bacterial consortia were investigated by combining different diuron-degrading bacteria (Sphingomonas sp. SRS2, Variovorax sp. SRS16, and Arthrobacter globiformis D47) and fungi (Mortierella sp. LEJ702 and LEJ703). The fastest mineralization of (14)C-labeled diuron was seen in the consortium consisting of Mortierella LEJ702, Variovorax SRS16, and A. globiformis D47, as measured by evolved (14)CO2. In addition, the production of diuron metabolites by this consortium was minimal. Analyses of 16S rDNA suggested that bacteria were transported more efficiently by LEJ702 than by LEJ703. Finally, it was determined that the fungal growth differed for LEJ702 and LEJ703 in the three-member consortia. This study demonstrates new possibilities for applying efficient fungal-bacterial consortia for bioremediation of polluted soil.

Determination of total organic halogen (TOX) in humic acids after microwave-induced combustion

Chemically chlorinated organic matter as well as natural background humic acids contain significant amounts of organically bound halogens that must be determined for assessment of environmental pollution. In this work the use of ion chromatography (IC) and inductively coupled plasma mass spectrometry (ICP-MS) is proposed for the determination of total organic Cl, Br and I concentration in humic acids extracted from various forest soil horizons after a single digestion by microwave-induced combustion (MIC). Samples were pressed as pellets and combusted using 20 bar of oxygen and ammonium nitrate solution as igniter. Analytes were absorbed in diluted alkaline solution (50mM (NH(4))(2)CO(3)) and a reflux step was applied after combustion to improve analyte recoveries (5 min, microwave power of 1400W). The accuracy was evaluated using certified reference materials (CRM) and spiked samples. Using MIC the agreement with CRM values and spike recoveries was higher than 97% for all analytes. As an advantage over conventional procedures, using MIC it was possible to digest up to eight samples in only 25 min, obtaining a single solution suitable for all halogens determination in humic acids samples by different techniques (IC and ICP-MS). The limit of detection (3σ) for Cl, Br and I obtained by IC was 1.2, 2.5 and 4.3μgg(-1) and by ICP-MS it was 1.4, 0.03 and 0.002μgg(-1), respectively.

Inhibition of DNA Polymerases Used in Q-PCR by Structurally Different Soil-Derived Humic Substances

Real-time PCR for the quantitative assessment of microbial genes in DNA extracted from environmental samples is increasingly being used in microbial ecology studies. A significant problem with the quantitative aspect of the method is the possible inhibition of the PCR process by humic substances co-extracted with the DNA. A comparison of the inhibition exerted by five structurally different humic substances on six commercially available DNA polymerases revealed large differences in the resistance of the polymerases to inhibition. Depending on the DNA polymerases (or their formulation) the addition of Bovine Serum Albumin (BSA) to the mastermix reaction generally increased the resistance to the different humic substances and decreased differences between the polymerases. One of the tested polymerases was clearly hampered by the addition of BSA, indicating that BSA cannot be added to just any mastermix to improve enzyme performance. The structural differences in the tested humic acids suggest that the mechanism of the inhibition is not a feature of all organic structures, but mainly related to the presence of certain phenolic or quinonoid structures.

Fungal hyphae stimulate bacterial degradation of 2,6-dichlorobenzamide (BAM).

Introduction of specific degrading microorganisms into polluted soil or aquifers is a promising remediation technology provided that the organisms survive and spread in the environment. We suggest that consortia, rather than single strains, may be better suited to overcome these challenges. Here we introduced a fungal-bacterial consortium consisting of Mortierella sp. LEJ702 and the 2,6-dichlorobenzamide (BAM)-degrading Aminobacter sp. MSH1 into small sand columns. A more rapid mineralisation of BAM was obtained by the consortium compared to MSH1 alone especially at lower moisture contents. Results from quantitative real-time polymerase chain reaction (qPCR) demonstrated better spreading of Aminobacter when Mortierella was present suggesting that fungal hyphae may stimulate bacterial dispersal. Extraction and analysis of BAM indicated that translocation of the compound was also affected by the fungal hyphae in the sand. This suggests that fungal-bacterial consortia are promising for successful bioremediation of pesticide contamination.

Intermediate accumulation of metabolites results in a bottleneck for mineralisation of the herbicide metabolite 2,6-dichlorobenzamide (BAM) by Aminobacter spp.

Degradation and mineralisation of the groundwater contaminant 2,6-dichloro-benzamide (BAM) was investigated in two Aminobacter strains focussing on the induction of BAM degradation and mineralisation and occurrence of intermediate metabolites. The BAM degradation rate was independent of whether the cells were pre-grown in the absence or presence of BAM, thus indicating that the first step in the degradation pathway was constitutively expressed. In contrast, 14CO2 production was stimulated when cells were pre-grown in the presence of BAM, suggesting that one or more of the subsequent steps in the degradation pathway were inducible. Accumulation of 2,6-dichlorobenzoate (DCBA) during degradation of BAM demonstrated that the first step involved amidase activity. Mass balance calculations and thin-layer chromatography coupled with autoradiographic detection indicated that degradation of DCBA and at least one unknown metabolite may comprise a bottleneck for BAM mineralisation by Aminobacter spp. The study thus provides novel information about the BAM degradation pathway and points to the involvement of unknown intermediate metabolites in degradation of this important groundwater contaminant.

Establishment of Bacterial Herbicide Degraders in a Rapid Sand Filter for Bioremediation of Phenoxypropionate-Polluted Groundwater.

ABSTRACT In this study, we investigated the establishment of natural bacterial degraders in a sand filter treating groundwater contaminated with the phenoxypropionate herbicides (RS)-2-(4-chloro-2-methylphenoxy)propanoic acid (MCPP) and (RS)-2-(2,4-dichlorophenoxy)propanoic acid (DCPP) and the associated impurity/catabolite 4-chlorophenoxypropanoic acid (4-CPP). A pilot facility was set up in a contaminated landfill site. Anaerobic groundwater was pumped up and passed through an aeration basin and subsequently through a rapid sand filter, which is characterized by a short residence time of the water in the filter. For 3 months, the degradation of DCPP, MCPP, and 4-CPP in the sand filter increased to 15 to 30% of the inlet concentration. A significant selection for natural bacterial herbicide degraders also occurred in the sand filter. Using a most-probable-number (MPN) method, we found a steady increase in the number of culturable phenoxypropionate degraders, reaching approximately 5 × 105 degraders per g sand by the end of the study. Using a quantitative PCR targeting the two phenoxypropionate degradation genes, rdpA and sdpA, encoding stereospecific dioxygenases, a parallel increase was observed, but with the gene copy numbers being about 2 to 3 log units higher than the MPN. In general, the sdpA gene was more abundant than the rdpA gene, and the establishment of a significant population of bacteria harboring sdpA occurred faster than the establishment of an rdpA gene-carrying population. The identities of the specific herbicide degraders in the sand filter were assessed by Illumina MiSeq sequencing of 16S rRNA genes from sand filter samples and from selected MPN plate wells. We propose a list of potential degrader bacteria involved in herbicide degradation, including representatives belonging to the Comamonadaceae and Sphingomonadales.

Assessing the role of trichloroacetyl-containing compounds in the natural formation of chloroform using stable carbon isotopes analysis

Chloroform (CHCl(3)) is an environmental contaminant widely distributed around world, as well as a natural compound formed in various aquatic and terrestrial environments. However, the chemical mechanisms leading to the natural formation of chloroform in soils are not completely understood. To assess the role of trichloroacetyl-containing compound (TCAc) in the natural formation of chloroform in forest soils, carbon stable isotope analyses of chloroform and TCAc in field samples and chlorination experiments were carried out. The isotope analysis of field samples have revealed that the δ(13)C value of natural chloroform (δ(13)C(mean)=-25.8‰) is in the same range as the natural organic matter (δ(13)C(mean)=-27.7‰), whereas trichloromethyl groups of TCAc are much more enriched in (13)C (δ(13)C(mean)=-9.8‰). A similar relationship was also observed for TCAc and chloroform produced by chlorination of natural organic matter with NaOCl. The strong depletion of (13)C in chloroform relative to TCAc can be explained by carbon isotope fractionation during TCAc hydrolysis. As shown using a mathematical model, when steady state between formation of TCAc and hydrolysis is reached, the isotope ratio of chloroform is expected to correspond to isotope composition of NOM while TCAc should be enriched in (13)C by about 18.3‰, which is in good agreement with field observations. Hence this study suggests that TCAc are likely precursors of chloroform and at the same time explains why natural chloroform has a similar isotope composition as NOM despite large carbon isotope fractionation during its release.

Bioaugmentation of rapid sand filters by microbiome priming with a nitrifying consortium will optimize production of drinking water from groundwater

Ammonium oxidation to nitrite and then to nitrate (nitrification) is a key process in many waterworks treating groundwater to make it potable. In rapid sand filters, nitrifying microbial communities may evolve naturally from groundwater bacteria entering the filters. However, in new filters this may take several months, and in some cases the nitrification process is never sufficiently rapid to be efficient or is only performed partially, with nitrite as an undesired end product. The present study reports the first successful priming of nitrification in a rapid sand filter treating groundwater. It is shown that nitrifying communities could be enriched by microbiomes from well-functioning rapid sand filters in waterworks and that the enriched nitrifying consortium could be used to inoculate fresh filters, significantly shortening the time taken for the nitrification process to start. The key nitrifiers in the enrichment were different from those in the well-functioning filter, but similar to those that initiated the nitrification process in fresh filters without inoculation. Whether or not the nitrification was primed with the enriched nitrifying consortium, the bacteria performing the nitrification process during start-up appeared to be slowly outcompeted by Nitrospira, the dominant nitrifying bacterium in well-functioning rapid sand filters.