Pentachlorophenol biodegradation—II : Anaerobic

The fate of pentachlorophenol (PCP) during anaerobic digestion of sewage sludge solids was tested in a three phase protocol. Phase I involved acclimation; Phase II investigated biodegradation in semicontinuous-flow, stirred-tank reactors at solids retention times of 10, 20 and 40 days; phase III assessed the importance of nonbiological removal mechanisms and collected additional data concerning the extent of biodegradation. PCP was found to inhibit methanogenesis in unacclimated cultures at concentrations in excess of 200 μg l⁻¹ and thus acclimation of the digesters to PCP required very gradual increases in the influent concentration thereby allowing enrichment of organisms capable of degrading PCP. Once acclimation was achieved, digesters receiving influent containing 5.0 mg l⁻¹ PCP achieved stable operation with effluent PCP concentrations below 5 μg l⁻¹ at all retention times studied. Sorption was shown to be unimportant in PCP removal. Volatilization was considered to be unimportant based upon results obtained in forced aeration studies. This suggested that PCP was subject to at least primary biodegradation. Other evidence collected during the study indicated that more complete biodegradation probably was occurring.     

Deoxygenation in a mobile-bed river—II. Model calibration and post-audit

Benthic metabolism accounts for over 90% of oxygen uptake in the Tarawera, a mobile-bed river receiving treated pulp mill effluent. A steady-state DO model was developed in 1984 which uses zero-order kinetics for benthic metabolism. During calibration a strong linear relationship was identified between the river deoxygenation rate (benthic oxygen uptake rate) and the river BOD concentration just below the main outfall. When tested against non-steady monitoring data the model successfully predicted monthly-average DO concentrations but tended to “overshoot” when waste loads varied. This suggests that the mobile-bed communities have some ability to attenuate the effects of varying waste loads. A post-audit of the model using recent monitoring data shows that the model can predict day-to-day variations of DO under average waste loading conditions but not when there are sudden large changes of waste load. It can be inferred that there are two different time scales operating: surface microbial communities respond quickly (1–2 days) to variations in waste load, but following a major reduction in waste load, reworking of deeper sediments depresses river DO for several weeks. There is a need to develop “biofilm” type models of mobile-bed rivers in order to refine predictions of DO under non-steady waste loadings.     

Chemical regeneration of exhausted activated carbon—II

This paper represents the second of a series of reports on the chemical regeneration of exhausted activated carbon following experimental research studies carried out at the University of Birmingham, U.K.

A wide range of regenerants, inorganic and organic, was evaluated in the treatment of carbon samples exhausted with 2-naphthol, 2-methoxyphenol, 2-chlorophenol, o-cresol and 2-nitrophenol, in order to compare the effects of the introduction of a second benzene ring (i.e. in effect the addition of C₄H₄, OCH₃, Cl, CH₃ and NO₂ groups to phenol on susceptibility to desorption.

There was a marked correlation between decreasing molecular weight of adsorbate and decreasing value of regeneration efficiency; the smaller the adsorbate, the further it could penetrate into the micropores of the carbon thereby resisting displacement by the regenerant. Furthermore, it was observed that, in general, the smaller the organic regenerant the further it could penetrate into the micropores of the carbon and displace the adsorbate. These complementary observations indicate that where chemical reactions are unlikely between organic regenerant and adsorbate, the success of the regeneration process is governed by the mechanism of physical displacement of the adsorbate molecule by the organic solvent molecule. The importance of the molecular weights and sizes of the adsorbate and the solvent is thus confirmed.     

Tunnels under pressure — mitigating the human response

The paper sets out initial findings from research into the current incidence of decompression illness in UK tunnelling. It comments critically on various measures used to quantify and compare the incidence of decompression illness and identifies the one most suited to current attitudes towards an individual's health risk. Possible reasons for the differences between current measures of DCI incidence and those based on historic data are explained. The innovative use, for research into decompression illness resulting from compressed air tunnelling work, of mathematical modelling techniques developed for hyperbaric research in the commercial diving industry is described, and results from early model studies are outlined.     

Virus concentration using hollow fiber membranes—II

An asymmetric polysulphone hollow fiber membrane permeator was used to concentrate polio I virus from 5 and 50-L of deionized- and tap-water. The objective of the study was to evaluate the effect of several independent variables—membrane type and morphology, initial virus concentration, initial feed volume, feed water type and backwash recovery of virus—on process performance. Also, it was the purpose of this study to compare performance for the asymmetric polysulphone and semidense symmetric cellulose acetate hollow fiber membranes (Belfort, Rotem and Katzenelson, 1975). From the results presented here and from a general chemical and biological stability point of view, the polysulphone membranes were superior for virus concentration. The module tested here proved to be versatile and continuously reusable. Finally, in no case and under all conditions studied was polio I virus detected in the permeate.     

软土地基静压预应力管桩挤土效应的防治

分析了预应力混凝土管桩软土地基的优缺点,以某住宅楼工程的桩基工程为例,探讨了挤土效应产生的机理,详细地阐述了减少静压桩挤土效应的措施,可供类似工程参考。     

Gas chromatography in water analysis—II selective detection methods

Gas chromatographic methods using selective detectors have been applied successfully to the determination of haloforms, herbicides and chlorophosphate esters in water extracts.

Electron capture detection has been used for the determination of the four haloforms, CHCl₃, CHCl₂Br, CHClBr₂ and CHBr₃ in pentane extracts. The very low detection limits render both the extracts and calibration solutions highly susceptible to contamination, and precautions necessary for their handling and storage are described.

Mass spectrometric single ion monitoring of gas chromatographic effluents has been used for the determination of the herbicides MCPA, MCPB and Mecoprop in methylated ether extracts. Possible interference from other components of the water extracts is discussed, and it is concluded that more than one ion should be monitored for each herbicide to minimise the interference.

A flame photometric method involving detection at 528 nm has been developed for the determination of chlorophosphate esters in dichloromethane extracts. The method is extremely specific for phosphorus compounds, but some interference from sulphur compounds may be observed. This can be minimised by the use of high efficiency capillary columns.

Detection limits and linear response ranges for the methods are given, and detector selectivities are discussed. Typical chromatograms are shown, and representative results for raw and treated waters are also given.     

Inorganic nitrogen removal in a combined tertiary treatment-marine aquaculture system—II. Algal bioassays

Algal bioassays were conducted on samples from various components of the combined tertiary treatment-marine aquaculture process, described in Part I of this study. These assays demonstrated that nitrogen removal is necessary to prevent increasing the algal growth potential of coastal marine waters receiving wastewater discharges. When nitrogen was removed from secondarily treated domestic wastewater, the wastewater in varying dilutions with seawater could not support more algal growth than the seawater alone. By adding nitrogen back to the treated wastewater the algal growth potential was increased to that of the untreated wastewater. This was demonstrated by assaying samples containing both artificially added nitrogen, and nitrogen regenerated by oysters. Assays of the effluent from the seaweed system showed that the removal of regenerated nitrogen reduced the algal growth potential to that of natural seawater.     

Soil/cement as a walling material—II. Some measures of durability

In the first paper a full factorial experiment designed to investigate changes in strength and strain characteristics was discussed. The main factors in the experiment involved changes in soil type, cement content and compaction pressure. This paper discussed the results from the same experiment using two measures related to durability as criterion variables. The first measurements recorded were of the initial surface absorption values and the second from a simplified freeze/thaw cycle test.     

Dynamics of the ozonation of phenol—II mathematical simulation

Several investigators have described the rate of ozonation of phenol in an ozone contactor by empirical equations which are system-specific and are limited in their applicability to other systems. In this paper, the rate of mass-transfer of ozone, the oxidation kinetics of phenol and the kinetics of formation and oxidation of the intermediates have been incorporated into a mathematical model which provides a more accurate picture of the process of oxidation of phenol by ozone under dynamic conditions.     

Effect of pulpmill effluent on dissolved oxygen in a stratified estuary—II. Numerical model

A numerical model is presented which simulates the biological and physical processes of oxygen supply in a stratified inlet. The results of the model show that the introduction of pulpmill effluent into the upper layer of the inlet causes a decrease in the dissolved oxygen concentration of the water due to blockage of photosynthesis in the stratum of water immediately below the halocline. Removal of the biochemical oxygen demand from the effluent has very little effect on the oxygen concentration in the upper layer since the supply of oxygen from the lower layer is blocked by the stain. Removal of 90 per cent of the stain from the effluent restores the oxygen concentrations to near normal.     

Physical aspect of flocculation process—II. Contact flocculation

Kinetic equations which describe the process of contact flocculation in solids contact clarifiers were proposed. Decrease of micro-flocs with the contact of high concentration and large diameter well-grown-flocs both in a turbulent flocculation chamber and in a floc blanket of upflow clarifier were discussed.First order equations with the micro-floc concentration were derived theoretically for both types of contact flocculation. By experiments, these kinetic equations were verified and their coefficients were evaluated.Finally, practical equations for the design of micro-floc removal process with the contact of well-grown-flocs both in a turbulent flocculator and in a floc blanket were proposed.     

Impact of western coal mining—II. Microbiological studies

The occurrence and activity of certain groups of sulfur cycle bacteria associated with waters, sediments, and the coal bearing strata of a coal strip mine at Decker, Montana, were studied. Mining areas in northeastern Wyoming were also examined.Thiobacillus ferooxidans, one of the major contributors to acid mine drainage, was consistently detected in the mining environment. Physiological studies of T. ferrooxidans isolates indicated that these acidophilic iron and sulfur oxidizing organisms were typical of the species in their preference for low pH and ability to oxidize pyrite. Since (i) acidic conditions were not observed at Decker, (ii) the organisms did not multiply in mine water environments and (iii) no acid could be formed from coal samples inoculated with a T. ferrooxidans isolate, it was thought that their activity was limited to microzones in the coal bearing strata where they oxidized sulfuritic material. Any acid formed was quickly neutralized by mineral carbonates associated with the groundwaters and overburden.Sulfate reducing bacteria also were common in the mine waters and sediments. These organisms were particularly active in the sedimentation pond sediments as was evidenced by the rapid rate of conversion of radio-labeled sulfate to sulfide. The hydrogen sulfide produced by these organisms contributed to heavy metal precipitation in the sedimentation pond.     

Effects of inorganic metal toxicity on bod—I methods for the estimation of bod parameters—II

Metal toxicity: In this study, the effects of HgCl₂, HgSO₄, K₂Cr₂O₇, CuSO₄, ZnSO₄ and Al₂(SO₄)₃ on BOD were investigated using a respirometer. When these inorganic metal compounds were added to a synthetic medium, respirometric BOD values and bacterial growth in an aeration system were affected. Parameter estimation: Some new solutions of the first order equation are time saving alternatives to the existing ones. Ultimate BOD values obtained from the second order equation are significantly higher than those produced from the first order equation. There is linear relationship between first and second order BOD parameters using crude sewage samples, but not when synthetic medium is used.     

Spring bloom in a hypereutrophic lake, lake Kasumigaura, Japan—II Succession of phytoplankton species

Numerous phytoplankton species in Lake Kasumigaura were shown to comprise the Spring bloom in 1980. The predominant phytoplankton species that appeared during the Spring bloom belonged to 28 genera. A few species among them increased at any time to form a phytoplankton pulse, but the few species of phytoplankters that comprised a phytoplankton pulse did not exclude completely other phytoplankters. During the Spring bloom, one pulse was replaced by another pulse composed of a new grouping of different species. Throughout these replacements by natural selection in the bloom were numerous other species by phytoplankters at levels of abundance somewhat less than those which formed phytoplankton pulse.     

Adsorption studies using gas-liquid chromatography—II. Competitive adsorption

Gas-liquid chromatography with a flame ionization detector system using the direct injection of aqueous solutions was used to monitor the adsorption of selected organic compounds dissolved in water onto activated carbon.The effects of competitive adsorption in batch (agitated flask) and column (flow through packed bed) systems were investigated. The effects became more pronounced with increase in the number of solutes in solution. This emphasises the importance of the competitive adsorption effect on the performance of an activated carbon unit in water or wastewater treatment.     

Outdoor algal mass cultures—II. Photosynthetic yield limitations

The photosynthetic conversion of sunlight energy into algal biomass in large-scale outdoor cultures is controlled by the availability of sunlight, the photosynthetic machinery of algae, nutrients, temperature and the design characteristics of the culture system. For the situation in which light is made the growth rate limiting factor, there is an upper limit in the light conversion efficiency of a large-scale culture, which translates to a maximum potential yield of 30—40g dry wt m² day¹ under ideal sunlight conditions. In practice, the best yield data for outdoor cultures in various locations in the world has been 30–40g dry wt m⁻² day⁻¹ for short periods and considerably less for longer durations. The development of large-scale mass cultures involves many considerations, but the two major design parameters for optimizing yields at a particular time of year are the flow rate through the culture and the depth.     

The electrolytic respirometer—II Use in water pollution control plant laboratories

The electrolytic respirometer provides a direct and continuous measure of oxygen uptake in a wastewater sample. The principal advantages of this method are that (1) little or no dilution of the sample is required, (2) larger and more representative samples can be analyzed, (3) tests can be run for days or weeks without interruption, (4) the equipment is simple to operate, (5) no titrations are required, and (6) BOD can be measured with significantly greater precision than with other methods.

The use of electrolytic respirometers in research laboratories and water pollution control plant and industrial laboratories demonstrated that the method is technically and economically justified for plant control and evaluation purposes. This method was well received by treatment plant operators and laboratory analysts when used for purposes ranging from routine measurement of BOD to investigating the treatability of industrial wastes.     

Total mercury and methyl mercury levels in British estuarine sediments—II

Results from a large-scale study of Mersey Estuary, U.K. sediments are discussed. Correlations are drawn between total mercury, methyl mercury, silt and organic carbon contents of the sediments. These correlations are compared to earlier results, and coefficients range from 0.55 to 0.94.The influence of redox potential and the sulphide content of a sediment on both the ambient level of methyl mercury and the extent of a growth and decay effect in methyl mercury levels in sediments after sampling is discussed. The results show that in an esturary (Clyde, U.K.) where sulphide levels vary from 0 to 8.5 mg g⁻¹ there is a maximum level of methyl mercury found at approximately 5.8 mg g⁻¹ sulphide, suggesting that sulphide concentrations may control methyl mercury levels.