Anaerobic codigestion of municipal solid waste and biosolids under various mixing conditions--II: Microbial population dynamics

Microbial population dynamics were evaluated in anaerobic codigesters treating municipal solid waste and sewage sludge. Ribosomal RNA based oligonucleotide probes were used to characterize changes in population abundance of syntrophic volatile fatty acid degrading bacteria and methanogens. Changes in community structure were linked to traditional performance parameters during the recovery of previously unstable codigesters induced by a reduction in mixing levels. Methanosarcina spp. were the most abundant aceticlastic methanogens in unstable codigesters with high acetate concentrations, while Methanosaeta concilii was dominant in stable systems with low levels of acetate. Growth of Syntrophobacter wolinii was enhanced during stabilization of a codigester with a well-developed population of Methanobacteriaceae, possibly because the presence of adequate numbers of these hydrogenotrophic methanogens encouraged the syntrophic oxidation of propionate. Mesophilic saturated fatty acid beta-oxidizing syntrophs were most abundant in previously unstable codigesters. One minimally mixed reactor became unstable after switching to continuously mixed conditions. After the switch, total archaeal abundance decreased sharply, though Methanobacteriaceae and Methanosarcina spp. levels increased as the fermentation became unbalanced. Based on the results presented here, mixing appears to inhibit the syntrophic oxidation of volatile fatty acids, possibly by disrupting the spatial juxtaposition of syntrophic bacteria and their methanogenic partners.     

Effect of temperature increase from 55 to 65 degrees C on performance and microbial population dynamics of an anaerobic reactor treating cattle manure

The effect of a temperature increase from 55 to 65 degrees C on process performance and microbial population dynamics were investigated in thermophilic, lab-scale, continuously stirred tank reactors. The reactors had a working volume of 31 and were fed with cattle manure at an organic loading rate of 3 g VS/l reactor volume/d. The hydraulic retention time in the reactors was 15 days. A stable reactor performance was obtained for periods of three retention times both at 55 degrees C and 65 degrees C. At 65 degrees C methane yield stabilized at approximately 165ml/g VS/d compared to 200 ml/g VS/d at 55 degrees C. Simultaneously, the level of total volatile fatty acids, VFA, increased from being below 0.3 g/l to 1.8-2.4 g acetate/l. The specific methanogenic activities (SMA) of biomass from the reactors were measured with acetate, propionate, butyrate, hydrogen, formate and glucose. At 65 degrees C. a decreased activity was found for glucose-, acetate-, butyrate- and formate-utilizers and no significant activity was measured with propionate. Only the hydrogen-consuming methanogens showed an enhanced activity at 65 degrees C. Numbers of cultivable methanogens, estimated by the most probable number (MPN) method, were significantly lower on glucose, acetate and butyrate at the increased operational temperature, while the numbers of hydrogenotrophic methanogens remained unchanged. No viable propionate-degrading bacteria were enriched at 65 C. Use of ribosomal oligonucleotide probes showed that an increase in temperature resulted in a decreased contribution of the rRNA of the domain bacteria from 74-79 to 57-62% of the universal probe, while the rRNA of the domain archaea, increased from 18-23 to 34-36%.     

Mobility and profiles of polychlorinated dibenzo-p-dioxins and dibenzofurans in sediment of Ya-Er Lake, China

The sediment of Ya-Er Lake had been heavily polluted by polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) from the former chloralkali industry. The total amounts of PCDD/Fs and I-TEQ decreased along the water flow direction and also decreased from top to bottom layers of sediment cores. Sediment of Pond 1 was dominated by PCDF. especially TCDF. In contrast, in the other four ponds, PCDD dominated in all layers and octachlorinated dibenzo-p-dioxin (OCDD) predominated in all of the homologues. When homologue profiles from sediments and water samples were compared using principal component analysis (PCA), the first two principal components represented 95.2% of the variance in the data. The first component explained 75.9% of the variance and the second one 19.3%. Two clusters were most distinct, presenting a shift in PCDD/Fs composition from PCDF to heptachlorinated dibenzo-p-dioxin (HpCDD) and OCDD in sediments and water from Pond I to Ponds 2-5. The pattern variation between Pond I and Ponds 2-5 in Ya-Er Lake was most likely due to the change of process in the chemical plant after the dams between the ponds were built. The results of the present study also showed that log Koc of PCDD/Fs calculated from data of sediment and water in the field were comparable with theoretical log Koc. The results also implied that the concentrations of PCDD/Fs in water and sediments could be predicted from each other by log Koc.     

A Regionally Applicable Model for Estimating Flow Velocity at Ungauged River Sites in the UK

Measurements of flow velocity are often required for a broad range of issues surrounding water-resource management, and a velocity-estimation method is therefore desirable where extensive field data are unavailable. This paper presents the development of a model for estimating flow velocity using readily available catchment characteristics, and flow and channel geometry data. The velocity equations were calibrated using UK data, so that their application at any river site in the UK is attainable. The calibrated equation uses the mean flow and the dimensionless magnitude of the flow on the day in question to estimate the mean reach velocity for flows at any river site in the UK.     

Degradation of parathion in seawater

The decomposition of parathion (O,O-diethyl-O-p-nitrophenylthiophosphate) in seawater has been followed in the laboratory. The influence of temperature, pH, salinity, and particulate matter on the degradation time and products is shown. Chemical hydrolysis as well as biodegradation occurred. The ratio of the two depends on the pretreatment of the water. During chemical hydrolysis dearylation and dealkylation occur. Biodegradation was observed through the disappearance of the organic nitro compounds. Among the degradation products dealkylated parathion was found to be stable against further hydrolysis and microbial degradation under environmental conditions.     

Two-step seismic limit state design procedure based on non-linear LRFD and dynamic response analyses

Recently, the limit state design (LSD) or performance-based design have got popularity in the field of building design in Japan as well as in other countries. In the two design methods the structural reliability theory plays an essential role in setting design criteria as well as demonstrating the target reliability level to society. However, the conventional load and resistance factor design (LRFD) has been basically formulated supposing that safety checking is done on the basis of linear assumption of member forces and displacement. Therefore, when applying the LRFD for seismic design, for more accurate treatment of the non-linearity, a new procedure has to be explored especially for the ultimate limit state. Although several procedures for the structural reliability evaluation, treating non-linear displacement responses, have been proposed, they require complex procedures that may not be used in the practical design process. Accordingly, for applying it to a seismic LSD format based on the probabilistic concept, it is essential to manage two important requirements at the same time, accuracy and simplicity of procedure. In the present study, a new design format using the following two-step procedure is proposed to maintain both accuracy and simplicity; (1) a non-linear LRFD formulation, and (2) a formulation based on non-linear dynamic response analysis. Also, two design examples are presented.     

Elemental analyses of pine bark and wood in an environmental study

Bark and wood samples were taken from the same individuals of Scots pine (Pinus sylvestris L.) from a polluted area close to a Cu-Ni smelter in Harjavalta and from some relatively unpolluted areas in western Finland. The samples were analysed by thick-target particle induced X-ray emission (PIXE) after preconcentration by dry ashing at 550 degrees C. The elemental contents of pine bark and wood were compared to study the impact of heavy metal pollution on pine trees. By comparison of the elemental contents in ashes of bark and wood, a normalisation was obtained. For the relatively clean areas, the ratios of the concentration in bark ash to the concentration in wood ash for different elements were close to 1. This means that the ashes of Scots Pine wood and bark have quite similar elemental composition. For the samples from the polluted area the mean concentration ratios for some heavy metals were elevated (13-28), reflecting the effect of direct atmospheric contamination. The metal contents in the ashes of pine bark and wood were also compared to recommendations for ashes to be recycled back to the forest environment. Bark from areas close to emission sources of heavy metal pollution should be considered with caution if aiming at recycling the ash. Burning of bark fuel of pine grown within 6 km of the Cu-Ni smelter is shown to generate ashes with high levels of Cu, Ni as well as Cd, As and Pb.     

Tracking natural organic matter (NOM) in a drinking water treatment plant using fluorescence excitation-emission matrices and PARAFAC

Natural organic matter (NOM) in water samples from a drinking water treatment train was characterized using fluorescence excitation emission matrices (F-EEMs) and parallel factor analysis (PARAFAC). A seven component PARAFAC model was developed and validated using 147 F-EEMs of water samples from two full-scale water treatment plants. It was found that the fluorescent components have spectral features similar to those previously extracted from F-EEMs of dissolved organic matter (DOM) from diverse aquatic environments. Five of these components are humic-like with a terrestrial, anthropogenic or marine origin, while two are protein-like with fluorescence spectra similar to those of tryptophan-like and tyrosine-like fluorophores. A correlation analysis was carried out for samples of one treatment plant between the maximum fluorescence intensities (F_max) of the seven PARAFAC components and NOM fractions (humics, building blocks, neutrals, biopolymers and low molecular weight acids) of the same sample obtained using liquid chromatography with organic carbon detection (LC-OCD). There were significant correlations (p < 0.01) between sample DOC concentration, UVA₂₅₄, and F_max for the seven PARAFAC components and DOC concentrations of the LC-OCD fractions. Three of the humic-like components showed slightly better predictions of DOC and humic fraction concentrations than UVA_254. Tryptophan-like and tyrosine-like components correlated positively with the biopolymer fraction. These results demonstrate that fluorescent components extracted from F-EEMs using PARAFAC could be related to previously defined NOM fractions and that they could provide an alternative tool for evaluating the removal of NOM fractions of interest during water treatment.     

Hybrid anion exchanger for trace phosphate removal from water and wastewater

Throughout recent decades, the wastewater treatment industry has identified the discharge of nutrients, including phosphates and nitrates, into waterways as a risk to natural environments due to the serious effects of eutrophication. For this reason, new tertiary treatment processes have abounded; these processes generally utilize physico-chemical and biological methods to remove nutrients from secondary wastewaters. The disadvantages of such methods involve larger reactor volumes, operating costs, and waste sludge production; furthermore, complete nutrient removal is unattainable due to thermodynamic and kinetic limitations. The subject study presents the development and performance of a new phosphate-selective sorbent, referred to as hybrid anion exchanger or HAIX. HAIX combines durability and mechanical strength of polymeric anion exchange resins with high sorption affinity of hydrated ferric oxide (HFO) toward phosphate. HAIX is essentially a polymeric anion exchanger within which HFO nanoparticles have been dispersed irreversibly. Laboratory studies show that HAIX selectively removes phosphate from the background of much higher concentrations of competing sulfate, chloride and bicarbonate anions due to the combined presence of Coulombic and Lewis acid-base interactions. Experimental results demonstrate that HAIX's phosphate-sulfate separation factor is over two orders of magnitude greater than that of currently available commercial ion exchange resins. Additionally, optimal HAIX performance occurs at typical secondary wastewater pH conditions i.e., around 7.5. HAIX is amenable to efficient regeneration and reuse with no noticeable loss in capacity.     

Reactor development for peroxidase catalyzed polymerization and precipitation of phenols from wastewater

Horseradish peroxidase enzyme catalyzes the oxidation of toxic aromatic compounds, especially phenols and aromatic amines, in the presence of hydrogen peroxide. The reaction products polymerize to form high molecular weight materials which readily precipitate from solution; hence, providing a means for the treatment of wastewaters which contain aromatic compounds. The catalytic lifetime of horseradish peroxidase enzyme can be extended by optimizing treatment conditions such as pH and temperature and by maintaining a low instantaneous enzyme concentration in the reaction mixture. The enzyme catalyzed polymerization process was implemented in a continuous stirred tank reactor (CSTR) configuration because reactant and enzyme concentrations are lowered immediately upon entering the reactor causing a reduction in inactivation of HRP through free radical bonding and compound III formation. Catalytic turnovers achieved in single and multiple CSTRs in series were significantly higher than those observed in batch reactors when sufficient retention time was provided.