The effect of an aldehyde biocide on the performance and characteristics of laboratory-scale rotating biological contactors

The effect of an aldehyde biocide, glutaraldehyde, on the treatment efficiency of laboratory-scale rotating biological contactors (RBCs) as well as their component biofilms was studied. Biofilms were established on the RBCs and then exposed to 0-120 ppm glutaraldehyde at a flow rate of 2.5 l x h(-1). The results showed that glutaraldehyde up to 80 ppm did not cause any adverse effect on chemical oxygen demand (COD) removal of the RBC units, microbial activity (ATP content) of biofilms on the RBC disc and viability of the biofilms. Glutaraldehyde at 80 ppm could be almost totally removed by the units regardless of the presence of simple carbon sources. There was at least a fourfold difference in susceptibility of planktonic and sessile bacteria to glutaraldehyde. Cells acclimatized to glutaraldehyde did not increase their capability to degrade normal carbon sources or glutaraldehyde under the conditions used in this study.     

Relationships among filamentous microorganisms in rotating biological contactors

The existing relationships were studied among the different types of filamentous microorganisms that appear in the biofilm of a biological contactor system. Using the hierarchical cluster analysis it was observed that, in all the stages, Beggiatoa sp. and the Eikelboom’s types 0803 and 1863 always appeared associated, while Sphaerotilus natans was always associated with the morphological type 021N. The remaining microorganisms were associated in variable forms in the plants. In addition, different association models were obtained according to the season of the year and the stage-season interaction. It has also been observed that a significant correlation exists among the filamentous microorganisms we have studied and the different physical-chemical parameters.     

The effect of a quaternary ammonium biocide on the performance and characteristics of laboratory-scale rotating biological contactors

AIMS: To study the effect of a quaternary ammonium biocide, didecyldimethylammonium chloride (DDAC), on the treatment efficiency of laboratory-scale rotating biological contactors (RBCs) as well as their component biofilms. METHODS AND RESULTS: Biofilms were established on the RBCs and then exposed to 0-160 mg l(-)1 (p.p.m.) DDAC at a flow rate of 2.5 l h(-1). The treatment efficiency of the RBC and the microbial activity of the biofilms were markedly decreased when 40 mg l(-1) DDAC or greater were applied to the units. However, DDAC had no effect on the number of viable bacteria in the biofilms when DDAC concentrations up to 80 mg l(-1) were applied to the RBCs. No viable bacteria could be detected in the biofilm when DDAC was applied at 160 mg l(-1). Extended observation over a further 40 d with 20 and 80 mg l(-1) DDAC showed similar results in terms of chemical oxygen demand removal, ATP content and viability of biofilms compared with those values over the first 12 d of exposure. CONCLUSIONS: There was at least a fourfold difference in the susceptibility of planktonic and sessile bacteria to DDAC. Cells acclimatized to DDAC did not increase their capability to degrade normal carbon sources or DDAC under the conditions used in this study. SIGNIFICANCE AND IMPACT OF THE STUDY: The results show that RBCs can be used to treat effluents containing DDAC at concentrations up to 20 mg l(-1) and that 160 mg l(-1) of DDAC was required to eliminate cells in established biofilms.     

Bioaugmentation of a rotating biological contactor for degradation of 2-fluorophenol

The performance of a laboratory scale rotating biological contactor (RBC) towards shock loadings of 2-fluorophenol (2-FP) was investigated. During a period of ca. 2 months organic shock loadings of 25 mg L?1 of 2-FP were applied to the RBC. As no biodegradation of 2-FP was observed, bioaugmentation of the RBC with a 2-FP degrading strain was carried out and, along ca. 6 months, organic shock loadings within a range of 25-200 mg L?1 of 2-FP were applied. Complete biodegradation of 50 mg L?1 of 2-FP was observed during operation of the reactor. The RBC showed to be robust towards starvation periods, as after ca. 1month of non-supply of the target compound, the reactor resumed 2-FP degradation. The inoculated strain was retained within the biofilm in the disks, as the 2-FP degrading strain was recovered from the biofilm by the end of the experiment, thus bioaugmentation was successfully achieved.     

Dynamics of protozoan and metazoan communities in a full scale wastewater treatment plant by rotating biological contactors

Performance of a full-scale wastewater treatment plant by rotating biological contactors (RBC) system was monitored during a year by physico-chemical and microbial characterisation. Six points along wastewater treatment were selected in the plant: three points along the water line (influent, sedimentation tank and effluent) and three points along RBC system (RBC1, RBC2 and RBC3). Although a large seasonal change in the values of physico-chemical parameters was observed, operation of the plant was optimal during all year (90% of removal in BOD5 and SS influent content). Microbial characterisation was approached by determining the structure and dynamics of protozoan and metazoan communities. Protozoa were the most abundant in all stages in the plant, heterotrophic flagellates being the most representative group in the water line and ciliates in the RBC system. The same seasonal preference was only observed for heterotrophic flagellates in the water line and green flagellates in the RBC system, both groups having highest abundances in summer and spring, respectively. Identification of ciliated protozoa populations rendered 58 species of ciliates in the plant. Most of these species are typical of aerobic wastewater treatment systems except three of them, which are cited for the first time in this type of ecosystems: Chaenea stricta, Holosticha mancoidea and Oxytricha lanceolata. Along the water line 34 species were identified, and half of them only appeared occasionally (once in all the study), while along the RBC system biofilms 55 species were observed, and the majority appeared permanently in this system. Our results indicate that the type of habitat, rather than the physico-chemical water parameters, was the primary factor in determining the different distribution of protozoan and metazoan communities in the plant. In RBC biofilms, the structure of ciliate protozoa community was found to be quite sensitive to changes in physico-chemical parameters, mainly to organic loading (BOD5) variations.     

Biodegradation and biological treatments of cellulose, hemicellulose and lignin: an overview

In nature, cellulose, lignocellulose and lignin are major sources of plant biomass; therefore, their recycling is indispensable for the carbon cycle. Each polymer is degraded by a variety of microorganisms which produce a battery of enzymes that work synergically. In the near future, processes that use lignocellulolytic enzymes or are based on microorganisms could lead to new, environmentally friendly technologies. This study reviews recent advances in the various biological treatments that can turn these three lignicellulose biopolymers into alternative fuels. In addition, biotechnological innovations based on natural delignification and applied to pulp and paper manufacture are also outlined. Electronic Publication     

A study on microbiology of biological film layer in rotating biological contactors

Experimental studies were carried out for upgrading the secondary treated domestic sewage effluent using the Rotating Biological Contactors (RBC) as an unit process in the premises of the existing water reclamation plant of Satellite Centre Building Complex of Indian Space Research Organisation at Bangalore. As part of these studies, a brief study was carried out on the microbiological aspects of the biological slime layer developed in the RBC. This study included observations on the development of the biological film on wetted disc surfaces of RBC, measurement of the thickness of the biological film, a discussion on significance of biofilm thickness in substrate removal, effect of wastewater characteristics on the thickness of biofilm and determination of MLSS/MLVSS ratio of biological film obtained in RBC reactor used for upgrading the secondary effluent. The results of these studies are presented in this paper. The results of identification of species of micro-organisms predominant in the biological slime layer in the RBC used for upgradation of secondary treated effluent are discussed separately in another paper.     

Biodegradation of acid blue-15, a textile dye,by an up-flow immobilized cell bioreactor

Acid blue-15, a complex and resonance-stabilized triphenylmethane (TPM) textile dye, resistant to transformation, was decolorized/degraded in an up-flow immobilized cell bioreactor. A consortium comprised of isolates belonging to Bacillus sp., Alcaligenes sp. and Aeromonas sp. formed a multispecies biofilm on refractory brick pieces used as support material. The TPM dye was degraded to simple metabolic intermediates in the bioreactor with 94% decolorization at a flow rate of 4 ml h^–1.     

Identification of micro organisms in the biological slime layer of rotating biological contactors

Bacterial samples and sludge from the RBC were taken from various points and intervals fixed properly and examined for the growth of microorganisms. The microorganisms in stage 1 to stage 4 were identified, described and discussed. The species present at different stages were compared with the microorganisms reported by other workers.     

Development of an obligate anaerobe specific biocide

Summary Anaerobic bacteria, such as sulfate-reducing bacteria and clostridia, are capable of generating H₂S and organic acids which corrode metallurgy resulting in millions of dollars of damage to industry annually. The bacteria are obligate anaerobes which grow typically on equipment surfaces under deposits such as biofilms. A successful method of penetrating biofilm and killing the anaerobic bacteria specifically has not been previously presented. We have investigated whether a blend of 1-(2-hydroxyethyl)-2-methyl-5-nitroimidazole (metronidazole) and a biodispersant would killDesulfovibrio, Desulfotomaculum, andClostridium species grown in the laboratory and in field applications. We found the blend significantly reduced the anaerobes in laboratory cultures. However, in a bioreactor designed to induced a high level of biofilm production and enhance underdeposit growth of anaerobic bacteria, a 40–58% increase in the antibiotic-biodispersant blend concentration was required. The metronidazole blend killed obligate anaerobic bacteria specifically but was non-toxic to aerobic bacteria and fungi. These results were confirmed in cooling tower field trial studies.     

Continuous bacterial ferrous iron oxidation by Thiobacillus ferrooxidans in rotating biological contactors

Summary Fe oxidation in rotating biological contactors has been studied over a range of influent Fe concentrations. Rotation speeds greater than 20 rpm did not affect the oxidation rate. Hydraulic loading rates above a critical value reduce the oxidation rat at influent Fe>4g/L.     

Rotating biological contactors: a review on main factors affecting performance

Rotating biological contactors (RBCs) constitute a very unique and superior alternative for biodegradable matter and nitrogen removal on account of their feasibility, simplicity of design and operation, short start-up, low land area requirement, low energy consumption, low operating and maintenance cost and treatment efficiency. The present review of RBCs focus on parameters that affect performance like rotational speed, organic and hydraulic loading rates, retention time, biofilm support media, staging, temperature, influent wastewater characteristics, biofilm characteristics, dissolved oxygen levels, effluent and solids recirculation, step-feeding and medium submergence. Some RBCs scale-up and design considerations, operational problems and comparison with other wastewater treatment systems are also reported.     

The effect of disk rotational speed on oxygen transfer in rotating biological contactors

Lab-scale experiments using a synthetic wastewater were carried out to assess the influence of disk rotational speed on oxygen transfer rate in a RBC unit in the presence of biomass. The overall oxygen transfer coefficient (K(L)a) was computed. Five different disk rotational speeds were tested, in the typical RBC operating range (3-10 RPM). The soluble organic substrate was monitored through TOC analysis. Influent hydraulic organic loadings were in the range of 5.4-35.2 g TOC/m(2)d. The set of kinetic coefficients calculated fitting the experimental data by the selected model resulted in good agreement with the value reported in literature. A correlation for K(L)a as a function of disk rotational speed and disk diameter was obtained. Accordingly, a new expression of the enhancement factor of oxygen transfer was found, and compared to literature data.     

Biodegradation of polyhydroxyalkanoates

Abstract Degradation of poly(3-hydroxybutyrate) and copolymers with 3-hydroxyvaleric acid was investigated in natural environments, and the microorganisms involved were isolated and identified. The influence of abiotic and biotic factors on the degradation is discussed.     

Adaptation of Pseudomonas sp. GJ1 to 2-bromoethanol caused by overexpression of an NAD-dependent aldehyde dehydrogenase with low affinity for halogenated aldehydes

Pseudomonas sp. GJ1 is able to grow with 2-chloroethanol as the sole carbon and energy source, but not with 2-bromoethanol, which is toxic at low concentrations (1 mM). A muatnt that could grow on 2-bromoethanol with a growth rate of 0.034 h^–1 at concentrations up to 5 mM was isolated and designated strain GJ1M9. Measurement of enzyme activities showed that mutant and wild-type strains contained a PMS-linked alcohol dehydrogenase that was active with halogenated alcohols and that was threefold overexpressed in the mutant when grown on 2-chloroethanol, but only slightly overproduced when grown on 2-bromoethanol. Both strains also contained an NAD-dependent alcohol dehydrogenase that had no activity with halogenated alcohols. Haloacetate dehalogenase levels were similar in the wild-type and the mutant. Activities of NAD-dependent aldehyde dehydrogenase were only slightly higher in extracts of the mutant grown with 2-bromoethanol than in those of the wild-type grown with 2-chloroethanol. SDS-PAGE, however, showed that this enzyme amounted to more than 50% of the total cellular protein in extracts of the mutant from 2-bromoethanol-grown cells, which was fourfold higher than in extracts of the wild-type strain grown on 2-chloroethanol. The enzyme was purified and shown to be a tetrameric protein consisting of subunits of 55 kDa. The enzyme had low K_m values for acetaldehyde and other non-halogenated aldehydes (0.8–4 μM), but much higher K_m values for chloroacetaldehyde (1.7 mM) and bromoacetaldehyde (10.5 mM), while V_max values were similar for halogenated and non-halogenated aldehydes. Cultures that were pregrown on 2-chloroethanol rapidly lost aldehyde dehydrogenase activity after addition of 2-bromoethanol and chloroamphenicol, which indicates that bromoacetaldehyde inactivates the enzyme. To achieve growth with 2-bromoethanol, the high expression of the enzyme thus appears to be necessary in order to compensate for the high K_m for bromoacetaldehyde and for inactivation of the enzyme by bromoacetaldehyde. Received: 31 August 1995 / Accepted: 4 December 1995     

Redox chemistry of biological tungsten: an EPR study of the aldehyde oxidoreductase from Pyrococcus furiosus

 Aldehyde:ferredoxin oxidoreductase (AOR) from the hyperthermophilic archaeon Pyrococcus furiosus is a homodimeric protein. Each subunit carries one [4Fe-4S] cubane and a novel tungsten cofactor containing two pterins. A single iron atom bridges between the subunits. AOR has previously been studied with EPR spectroscopy in an inactive form known as the red tungsten protein (RTP): reduced RTP exhibits complex EPR interaction signals. We have now investigated the active enzyme AOR with EPR, and we have found an S = 1/2 plus S = 3/2 spin mixture from a non-interacting [4Fe-4S]¹⁺ cluster in the reduced enzyme. Oxidized AOR affords EPR signals typical for W(V) with g–values of 1.982, 1.953, and 1.885. The W(V) signals disappear at a reduction potential E _m,7.5 of +180 mV. This unexpectedly high value indicates that the active-site redox chemistry is based on the pterin part of the cofactor. Received: 18 December 1995 / Accepted: 26 March 1996     

Effect of substrate concentration on biodegradation of 2,4-dichlorophenol using modified rotating biological contactors

2,4-Dichlorophenol used in the manufacture of pesticides, germicides, resins, seed disinfectants and antiseptics, if disposed untreated causes greater havoc for land and aquatic environment. In all the earlier works, 2,4-dichlorophenol has been fed along with easily biodegradable substrate, glucose as one of the constituents. A modified 4-stage RBC was used for the biodegradation studies of 2,4-dichlorophenol. The micro organisms attached to the disks were specially acclimatised to the extent that the 2,4-dichlorophenol alone serves as the sole carbon source supporting their metabolic activities. The RBC was operated at 12?rpm. The toxic substrate removal studies were carried out in the hydraulic loading rates ranging from 0.005?m³/m²/d to 0.035?m³/m²/d and organic loading rates from 0.35?g/m²/d to 6.15?g/m²/d. A correlation plot between 2,4-dichlorophenol removal and organic loading rate is presented. A mathematical model is proposed using regression analysis.     

Low-ammonia niche of ammonia-oxidizing archaea in rotating biological contactors of a municipal wastewater treatment plant

The first step of nitrification is catalysed by both ammonia-oxidizing bacteria (AOB) and archaea (AOA), but physicochemical controls on the relative abundance and function of these two groups are not yet fully understood, especially in freshwater environments. This study investigated ammonia-oxidizing populations in nitrifying rotating biological contactors (RBCs) from a municipal wastewater treatment plant. Individual RBC stages are arranged in series, with nitrification at each stage creating an ammonia gradient along the flowpath. This RBC system provides a valuable experimental system for testing the hypothesis that ammonia concentration determines the relative abundance of AOA and AOB. The results demonstrate that AOA increased as ammonium decreased across the RBC flowpath, as indicated by qPCR for thaumarchaeal amoA and 16S rRNA genes, and core lipid (CL) and intact polar lipid (IPL) crenarchaeol abundances. Overall, there was a negative logarithmic relationship (R(2) =?0.51) between ammonium concentration and the relative abundance of AOA amoA genes. A single AOA population was detected in the RBC biofilms; this phylotype shared low amoA and 16S rRNA gene homology with existing AOA cultures and enrichments. These results provide evidence that ammonia availability influences the relative abundances of AOA and AOB, and that AOA are abundant in some municipal wastewater treatment systems.     

Persister cells in a biofilm treated with a biocide

This study investigated the physiology and behaviour following treatment with ortho-phthalaldehyde (OPA), of Pseudomonas fluorescens in both the planktonic and sessile states. Steady-state biofilms and planktonic cells were collected from a bioreactor and their extracellular polymeric substances (EPS) were extracted using a method that did not destroy the cells. Cell structure and physiology after EPS extraction were compared in terms of respiratory activity, morphology, cell protein and polysaccharide content, and expression of the outer membrane proteins (OMP). Significant differences were found between the physiological parameters analysed. Planktonic cells were more metabolically active, and contained greater amounts of proteins and polysaccharides than biofilm cells. Moreover, biofilm formation promoted the expression of distinct OMP. Additional experiments were performed with cells after EPS extraction in order to compare the susceptibility of planktonic and biofilm cells to OPA. Cells were completely inactivated after exposure to the biocide (minimum bactericidal concentration, MBC = 0.55 ± 0.20 mM for planktonic cells; MBC = 1.7 ± 0.30 mM for biofilm cells). After treatment, the potential of inactivated cells to recover from antimicrobial exposure was evaluated over time. Planktonic cells remained inactive over 48 h while cells from biofilms recovered 24 h after exposure to OPA, and the number of viable and culturable cells increased over time. The MBC of the recovered biofilm cells after a second exposure to OPA was 0.58 ± 0.40 mM, a concentration similar to the MBC of planktonic cells. This study demonstrates that persister cells may survive in biocide-treated biofilms, even in the absence of EPS.