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.     

铝电解厂房自然通风的影响因素分析

通过模拟计算研究了架空层位于地面之上和地面之下这两种常见的2层结构铝电解厂房的自然通风效果。结果表明,架空层位于地面之下时,地面阻挡对进风口风量有很大影响,当凹槽宽度为1 m时,总风量约减少45%;宽度为3 m时,影响较小,风量约减少9%;宽度为3.5 m时,阻挡的影响可忽略。     

Factors affecting pH change in alkaline waste water treatment—I

The pH of wastewater in various stages of its purification depends mainly upon the equilibria of carbonic acid. Thus relations between pH and the concentrations of carbon dioxide, bicarbonate and carbonate can be formulated. Corrections for the non-ideal character of the sewage are necessary.

With some restrictions the concept of alkalinity can be used for these pH relations.

Several (bio)chemical and physical processes occurring in biological purification affect the concentrations of carbon dioxide and (bi)carbonate.

Processes studied are carbon dioxide desorption, oxidation of organic matter and nitrification.

Models are proposed for the calculation of the effluent pH and the values so obtained are compared with the available experimental results.     

Some factors affecting oxygen index of polyester fibres

A simple fibre sample holder was applied to the oxygen index test to determine the relative flammability of filament yarns. This modification permitted the study of the effects of sample weight and position on the oxygen index (OI) of polyester fibres. In order to characterize these effects, extrapolation of the OI curves to a zero weight of a sample (intrinsic oxygen index [OI]) and introduction of a weight factor (wf) were suggested. For the control 3 tex poly(ethylene terephthalate) (PET) monofilament tested in a vertical and horizontal position, the obtained values were, respectively, [OI]_ver = 0.175, wf_ver = 0.06 g⁻¹ and [OI]_hor = 0.174, wf_hor = 0.002 g⁻¹. The respective parameters for the flame-retardant 3 tex Heim monofil fibres were [OI]_ver = 0.192, wf_ver = 0.11 g⁻¹, [OI]_hor = 0.198, and wf_hor = 0.10 g⁻¹; and for the 3 tex PET monofil containing 5 phr Flammex B10-, [OI]_ver = 0.189, wf_ver = 0.03 g⁻¹, [OI]_hor = 0.174, and wf_hor = 0.06 g⁻¹.     

Effect of pulpmill effluent on dissolved oxygen in a stratified estuary—I. Empirical observations

Pulpmill effluent discharged at the surface in Alberni Inlet is shown to prevent oxygen production in the stratum immediately beneath the halocline by restricting light penetration. This stratum is the source of marine water for entrainment in the halocline and to the upper mixed zone. This situation cannot be remedied by removal of BOD from the pulpmill effluent, rather the staining properties must be diminished or removed.     

Pentachlorophenol biodegradation—I: Aerobic

The biodegradation of pentachlorophenol (PCP) was tested in a three phase protocol. Phase I involved acclimation; phase II allowed determintion of biodegradation kinetics through use of continuous stirred tank reactors (CSTR) operated at solids retention times of 3.2, 7.8, 12.8 and 18.3 days; phase III assessed the importance of volatilization and sorption in PCP removal and evaluated the extent of biodegradation. Over the range of SRT's studied, PCP was found to be biodegradable with first order kinetics; the rate constant (μ_m/K_s) had a value of 0.0017 l μg⁻¹d⁻¹. The minimum concentration of PCP attainable in a CSTR was found to be 27 μg l⁻¹. Additional studies suggested that the full relationship between the PCP degradation rate and the PCP concentration followed an inhibition-type function, with the maximum rate occurring at a PCP concentration of around 350 μg l⁻¹. Radioisotopic studies revealed that PCP was mineralized by the culture, with the liberation of CO₂ and the incorporation of carbon into cell material. Neither volatilization nor sorption removed significant amounts of PCP from the reactors.     

Nitrification in rotating disc systems—I: Criteria for transition from oxygen to ammonia rate limitation

Identification of the rate limiting substrate and half-order rate constants are presented on the basis of biofilm kinetics for triple substrate conditions (organic matter, ammonia and oxygen) in a rotating biological disc system. These findings have been verified by pilot-scale experiments. The transition from ammonia rate limitation to oxygen rate limitation occurs at a bulk ammonia-nitrogen concentration to bulk oxygen concentration ratio of approx. 0.4. Accordingly, oxygen is the rate limiting substrate. For most practical purposes the experiments showed that the oxygen limited half-order reaction constant in the presence of simultaneous organic matter degradation is reduced compared to nitrification alone by a factor which is a function of the growth of the heterotrophs and the nitrifiers in the biofilm.     

The accuracy of oxygen flux measurements using microelectrodes

An electrochemical analog of a biofilm was constructed to test the accuracy of oxygen flux measurements using microelectrodes. We used a cathodically polarized graphite felt attached to the bottom of a flat plate open channel reactor as the reactive surface consuming oxygen. The oxygen flux to the felt was calculated from the polarization current. Microelectrodes were used to measure the oxygen profiles above and within the graphite felt. From the shape of the oxygen profile we evaluated the oxygen flux to the graphite felt. This provided us with two sets of data, the true oxygen flux, calculated from polarization current, and the oxygen flux estimated from microelectrode measurements. Comparing these two fluxes, for different flow velocities, showed that the fluxes evaluated from the polarization current were different from those evaluated from the oxygen profiles. The differences were likely caused by the presence of the microelectrode in the mass boundary layer and/or by the simplifying assumptions accepted in computational procedures employed to calculate oxygen fluxes. For low flow velocities, between zero and 1.0 cm s⁻¹, the differences were velocity sensitive; the higher the flow velocity, the bigger the difference. For higher flow velocities, between 1 cm s⁻¹ and 3 cm s⁻¹, the flux of oxygen estimated from the microelectrode measurements was consistently approximately 80% higher than the true oxygen flux estimated from the polarization current.     

The treatment of woolscour effluent—I removal of colloidal dirt

A small group of synthetic polymeric flocculants have been found which are capable of flocculating colloidal dirt in woolscour effluent. Their effectiveness has been tested in both laboratory and fullscale experiments. It has been found that up to 80% of the dirt in the liquor may be removed, as a 20 w/v% solids sludge, which is readily de-waterable, using a solid bowl centrifuge, to 45–50% solids. Use of the flocculants in a recycle process had no deleterious effect on grease recovery or wool quality, but allowed a constant low discharge flow of liquor to be maintained, independent of the wool throughput or dirt content.     

Effect of inorganic constituents on chemical oxygen demand—I. Bromides are unneutralizable by mercuric sulfate complexation

Chemical oxygen demand (COD) assays are widely used for the estimation of the organic carbon content of water and wastewater. The procedure is subject to interference by free halogen ions, the oxidation of which creates artificially high COD values. As part of an investigation of the interferences involved in the COD determination of chemical industries wastewaters, we found that mercuric sulfate complexation, the standard procedure for neutralizing the halogen effects, is suitable for chlorides but is not applicable to bromides. This observation is true both in the presence or absence of chloride or ammonia. Care should therefore be exercised in the interpretation of COD data for bromide-containing samples.     

The ecology of a land drainage channel—I. Oxygen balance

In shallow land drainage channels day-time solar heating during the summer produced vertical temperature and density gradients. These facilitated the development of marked gradients of dissolved oxygen, with maximum sub-surface values exceeding 300% air saturation and deoxygenated water near the sediments. Night-time cooling promoted mixing of the water column. Rates of community photosynthesis and respiration, calculated from dissolved oxygen distributions by two methods, were high.     

Chemical regeneration of exhausted activated carbon—I

This paper represents the first 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 mono-substituted benzene compounds. Organic chemical regenerants with solubilising powers were found to be generally much more effective than inorganic chemical regenerants with oxidising powers. Results showed that the efficacy of organic solubilising regenerants decreased as their molecular weights and sizes increased; it is likely that the smaller the regenerant, the further it could penetrate into the micropores of the carbon and displace the adsorbate. The relationship between the molecular weight of the adsorbate and that of the organic regenerant was observed to be of significant importance; the regenerant chosen should be smaller than the smallest adsorbate to be removed.     

The dissolved oxygen profile—A valuable tool for control of the activated sludge process

Control of activated sludge process based on measurement of the dissolved oxygen profile has the distinct advantage of using sensors of proven reliability. These measurements, when coupled with the power of an on-line computer, permit the calculation of important variables which cannot be measured directly. The features of the profile which are of major significance are the position of the maximum slope, the value of the maximum slope, the DO concentration at the reactor outlet, the slope of the profile close to the outlet, and the second derivative of the profile towards the outlet. This paper demonstrates that the above mentioned features reflect both the hydraulic and organic loading, reaction rates, and degree of completion of the reactions in the activated sludge process. Simulations are presented to show how these features may be controlled by manipulating the mass of sludge in the reactor and the overall oxygen transfer rate coefficient.     

The removal of acid dye from effluent using natural adsorbents—I peat

The adsorption of Telon Blue (Acid Blue 25) on peat has been investigated. Adsorption parameters for the Langmuir and Freundlich isotherms were determined and the effects of contact time, initial dye concentration and peat particle size were studied. A series of fixed bed experiments were performed and the results compared with existing design models for adsorption columns.     

Sunlight requirements in buildings—I. Social survey

A social survey was conducted in four types of buildings, i.e. housing, schools, offices and hospitals. Surveys of existing literature, depth interviews, pilot studies and in some cases a postal survey were carried out before the structured questionnaire was finally formulated. Responses to the interviews were then analysed and computed. Brief conclusions are given in this paper. A more detailed analysis of results and conclusions will be reported later. The proposed recommendations for sunlight in buildings arising from the survey have been already published in the June 1976 issue of this Journal.     

Aquacultural approaches to recycling of dissolved nutrients in secondarily treated domestic wastewaters—I Nutrient uptake and release by artificial food chains

Wastewater based artificial food chains composed of sequential monocultures of a suspended unicellular green alga, of an herbivorous cladoceran crustacean, and of an herbivorous or a carnivorous teleost fish and of filamentous green algae were studied in an effort to find efficient, potentially economically viable mechanisms for the biological capture (tertiary treatment) of nutrients (especially nitrate and phosphate) in wastewaters processed by small to medium size two-stage treatment plants that primarily handle domestic and agricultural wastes.All experiments were carried out on laboratory scale systems with a low technology approach to keep apparatus and procedures as simple and reliable as possible.Among all organisms tested as components of the artificial food chains only the unicellular green alga Scenedesmus, the filamentous green algae Cladophora and Ulothrix, the cladoceran crustaceans Daphnia magna and Daphnia pulex, and the teleost fishes Notemigonus crysoleucas, Pimephales promelas and Notropis lutrensis were found to be suitable.Unmodified secondarily treated domestic effluents were both iron deficient and lacking in buffering capacity necessary for optimal algal growth. Additions of both ferrous iron (1 ppm) and carbon dioxide (5%) were required to achieve good quality cultures suitable for feeding cladocerans. Most removal of nutrients occurred in the first algal stage of the food chain. Nitrate removal averaged 78%, phosphate removal 55% in buffered algal cultures. In unbuffered cultures nitrate removal was 30%, phosphate removal 98%. The near complete removal of phosphate in unbuffered algal cultures was probably due to physico-chemical precipitation of phosphate complexes formed as a result of high pH levels (pH > 10) reached within 24 h of culture initiation. Cladoceran and fish stages added nutrients (mostly ammonia and phosphate) back into the effluent. A final stage of Ulothrix and Cladophora algae removed nutrients regenerated by cladocerans and fishes. A 12 h light–12 h dark cycle statistically significantly reduced levels of nutrient removal by both unbuffered and buffered algal cultures below removal rates measured in algae cultured in continuous light. Daily harvesting rates of 25–75% of culture volumes had no significant effect upon removals of nitrate by buffered algal cultures; phosphate removals were inversely proportional to harvesting rates in these cultures.Important theoretical and technical points are discussed.     

Inorganic nitrogen removal in a combined tertiary treatment—marine aquaculture system—I. Removal efficiences

The increasing awareness that nitrogen is often a key nutrient controlling algal growth in coastal marine waters has led to a concerted effort to find ways to remove ammonia and nitrate from wastewaters. A novel approach to this problem involves the combining of algal and seaweed nutrient stripping processes with a marine aquaculture. Not only is nitrogen removed from wastewater, but important commercial shellfish and seaweeds are produced.A prototype process consisting of growth systems for marine algae, oysters and seaweed, joined in series, was fed secondarily treated wastewater, diluted 1:4 with seawater, for 11 weeks during the Summer of 1972. During this time 95 per cent of the influent inorganic nitrogen was removed by algal assimilation. The oysters in turn removed 85 per cent of the algae, but regenerated as soluble ammonia 16–18 per cent of the nitrogen originally bound in the algal cells. All of the regenerated nitrogen was removed in the seaweed system so that the total inorganic nitrogen removal efficiency of the system was 95 per cent. Phosphorus removal on the other hand was not nearly as complete as only 45–60 per cent was removed.The process has the capability of being expanded to include additional trophic levels in an integrated and highly controlled food chain system to serve the dual function of tertiary wastewater treatment and waste recycling through the production of shellfish and seaweeds.     

半刚性基层冲刷唧浆的影响因素与防治措施

针对半刚性基层的广泛应用,分析了半刚性路面基层冲刷唧浆的产生原因,探讨了冲刷唧浆对路面的破坏作用,研究了半刚性基层冲刷唧浆的影响因素,从设计和施工两方面提出了防治半刚性基层冲刷唧浆的措施.