Contact Stabilization Research Articles

Phase and structural study of clathrate formation in the [Zn(MePy)2(NCS)2]-MePy system (MePy=4-methylpyridine)

A phase diagram of the [Zn(MePy)2(NCS)2]-MePy binary system has been studied by DTA and solubility methods. Two compounds melting incongruently (at 63 and 57°C) have been discovered in the system. They have been obtained as separate phases with crystals of different shape (needles and octahedra). Their composition has been determined by analytical methods and verified by X-ray structural analysis: [Zn(MePy)4(NCS)2]·0.67 MePy·xH2O, wherex depends on the synthesis conditions, and [Zn(MePy)4(NCS)2]·MePy, respectively. The preliminary X-ray study of the first compound (at −100°C) has shown it to be isostructural with the known clathrates of the common formula [M(MePy)4(NCS)2]·0.67MePy·xH2O, where M=Cu, Mn, Mg andx=0–0.33. The unit cell parameters are as follows:a=27.20(1),c=11.202(4) A, space group $$R\bar 3$$ ,Z=9. The X-ray study of [Zn(MePy)4(NCS)2]·MePy (at−50°C) has shown it to be analogous to the ‘organic zeolite’ β-phase with the guest MePy molecules located in the channels formed by molecular packing of the [Zn(MePy)4(NCS)2]host. The cell is tetragonal, the space groupI41/a,a=16.845(6),c=23.496(7) A,V=6667(4) A3,Z=8,D calc=1.289 g cm−3,R=0.074. The zinc cation is surrounded by a slightly irregular octahedron of six nitrogen atoms of the MePy and NCS ligands. The crystallisation field of the host [Zn(MePy)4(NCS)2] complex in the temperature range concerned is absent in the phase diagram. It suggests contact stabilization of the [Zn(MePy)4(NCS)2] molecule by the guest in the clathrates.

Improvement of Dewatering Characteristics of Aerobically Digested Sludges

The aim of this study was to evaluate the influence of both sludge characteristics and operational parameters on polymer selection and optimal dose requirements to improve the dewatering characteristics of aerobically digested sludges of a contact stabilization activated sludge plant in Jeddah, Saudi Arabia. In order to determine the dewatering characteristics of the sludge samples, capillary suction time (CST) and specific resistance to filtration (SRF) were measured. Cationic conditioning polymers were found more effective than the anionic types. The optimum polymer dose was equal to 4.2 kg of polymer/ton of dry matter for three of the cationic polymers used in this study namely Zeetag 57, Superfloc C420, and Zeetag 92. The optimum dose requirements are increased substantially with increasing pH values. A linear relationship was found between the optimal polymer dose in mg/l and the sludge solids concentration. The optimum total mixing time was found to be 2 min: 30 sec of rapid mixing at 100 rpm and 90 sec of slow mixing at 40 rpm. The sludge temperature variations were found to have a slight effect on polymer dose requirements. A linear relationship was obtained between the CST and SRF with a correlation coefficient of 0.99.

Regeneration of activated sludge under oxic and anoxic conditions

Regeneration of biomass cultivated by synthetic soluble organic substrate under oxic and anoxic conditions was studied by following the maximum substrate removal rates r x, m during the endogenous phase. Two semicontinuously operated units simulating contact stabilization process were operated. In one of the units endogenous anoxic period was established after nitrification was completed. The regeneration process was connected with an increase in r x, m values. The increase was very similar under both oxic and anoxic conditions. The comparison of the contact stabilization process with oxic and combined oxic-anoxic endogenous phase has shown the following: rates of exogenous substrate removal and nitrification were the same, in ox-anox system nitrogen was completely eliminated and oxygen consumption was reduced, the rate of regeneration was the same in both systems. Combined oxic-anoxic regeneration phase can be used as a modification of the contact stabilization process for soluble organic substrate. In addition, during the endogenous phase kinetic constants r x, m , saturation coefficient K 5, and biomass yield coefficient Y have significantly increased. The problem of actual Y value determination is discussed.

Rapid Removal of Colloidal Organics from Domestic Wastewater

Batch experiments were conducted with raw wastewater and preaerated microbial sludge to investigate the removal behavior of the contact stabilization activated sludge process. This process was originally developed based on observed rapid drops in BOD which were attributed to rapid adsorption of colloidal organics. To date no data have been presented verifying that rapid colloidal adsorption occurs or is responsible for rapid BOD decreases. Food to Microorganism (F:M) ratios were varied from 0.047 to 0.447 mg COD/mg MLSS during batch tests conducted with thirty minute contact times. Mixed liquor samples were collected at predetermined times, poisoned with mercuric chloride to halt microbial activity, and settled. Samples of the supernatant were drawn off and the COD of organics in different size ranges determined using a sequential filtering technique. Colloidal COD was defined to be the difference between the COD of organics passing a 1.5 µm filter and those passing a 0.03 µm filter. Results indicated that rapid colloidal removal occurred. Colloidal COD concentrations decreased from initial values (maximum 85 mg/l) to near 0 mg/l within five minutes after mixing. Such behavior was only observed for the colloidal fraction and occurred regardless of the initial colloidal COD, total COD, or F:M ratio. It was concluded that physical coagulation was most likely the mechanism responsible for rapid colloidal removal.

Recharging a potable water supply aquifer with reclaimed wastewater in Cambria, California

Water supply and delivery as well as wastewater collection and treatment in Cambria are provided by the Cambrla Community Services District (District). The wastewater treatment plant is a small contact stabilization activated sludge plant. The District currently disposes of its effluent in dedicated spray disposal fields located two and one half miles north of the treatment plant. The potable water for the community is supplied by two aquifers, Santa Rosa Creek aquifer and San Simeon Creek aquifer.

Economical pollution control in warm climates by contact stabilization wastewater treatment

Water pollution abatement with economical solutions, for wastewater treatment plants design and operation, is a crucial problem, especially for economically developing countries. The purpose of this study is the evaluation of the contact stabilization process to achieve economical secondary treatment as well as partial nitrification under favorable temperature conditions. The examined variables are easily definable parameters of practical importance for any wastewater treatment plant. Based on full scale plants data, correlations between design or operation variables and plant performance or effluent quality are reported.

Contact Stabilization of Host Molecules during Clathrate Formation

The occurence of contact stabilization of molecules during clathration is considered; non-bonded host–guest interactions may alter considerably the structure of the host molecules and may even lead to the stabilization of host molecules that do not exist outside the clathrate.

A simple, conceptual mathematical model for the activated sludge process and its variants

A simple structured kinetic model is applied to the activated sludge process. The objective is less to predict exact process performance than to illustrate some of the possibilities and difficulties in producing a comprehensive model for all the process variants. The rate equations are chosen so as to reduce to the Monod equation during balanced growth. Because these rate equations are linear, the cell growth and substrate uptake in a stirred tank can be defined exactly in terms of the average composition of the biomass. It is shown that this is not valid for other forms of rate equations. The stored substrate to protoplasm ratio in the flocs is found to decrease with increasing mean cell residence time. If extracellular biopolymers are included in the stored substrate this corresponds qualitatively to observations of poor flocculation in extended aeration. The model is also applied to the contact stabilization process and is found to be in agreement with the essential process variables.

Fine‐Pore Diffuser Retrofit at Midgewood, New Jersey

The Ridgewood Wastewater Treatment Plant in Ridgewood, New Jersey underwent a retrofit from a coarse‐bubble to fine‐pore aeration system. Also, process modification from contact stabilization to tapered air occurred. This paper provides a review of the case history of plant and aeration performance of each system from 1981 through 1986. Non‐steady state and off‐gas oxygen transfer field testing at the plant over the 6‐yr period provides the data base for the objective evaluation. An economic evaluation of retrofit impact is presented. Oxygen transfer efficiency of the fine pore system was approximately double that of the coarse bubble system. However, power costs were not reduced proportionately since a higher oxygen demand was supplied by the fine pore system to attain nitrification and meet the revised permit requirements. Severe nocardia foaming problems were encountered in the summer during the first three years of fine pore operation. These were controlled in the last two years by minimizing sludge recycle loads and preventing septic conditions in the aeration tanks.

Effect of the endogenous phase duration on the maximum substrate removal rate in mixed cultures

The maximum substrate removal rates, r x, m , were measured during the endogenous phase by means of a simple respirometric method. Excess biomass from a continuously-fed completely mixed (CM) and a semicontinuously-fed (SE) reactor was tested with ethylalcohol, glutamic acid, phenylalanine, acetic acid, phenol and glucose. It was found with the mixed culture from the CM system that during a 6-h endogenous period, the r x, m values remained constant with all the substrates tested. With the mixed culture from the SE system, the r x, m values increased during first 8–12 h of the endogenous period and then decreased. The authors conclude that the respirometric method measuring r x, m values can be used to optimize the contact stabilization process.

Contact stabilization of potential calcium carbonate scale by rhodochrosite

The mineral rhodochrosite (MnCO 3) causes rapid precipitation of calcium carbonate when it is added to seawater. The calcium carbonate forms a solid solution of the type Mn 1− x Ca x CO 3 on the rhodochrosite surface. As a result, seawater becomes undersaturated with respect to pure calcite. The degree of saturation ranged from 0.42 to 0.10, and it is a function of the solid to liquid ratio. Seawater that has been equilibrated with rhodochrosite can, therefore, be concentrated substantially before it again becomes supersaturated with respect to calcite. Potential calcium carbonate scale is also reduced by equilibrating seawater with rhodochrosite.

Operation and Performance of a New Activated Sludge Process: The Contact Stabilization Extended Aeration Hybrid

In this study the operation and performance of a contact stabilization process operating under the extended aeration mode is examined. Data was obtained during a detailed plant study carried out at a full scale municipal wastewater treatment plant. This new hybrid activated sludge process has good process stability like the conventional extended aeration process, but achieves this with a significantly smaller aeration tank volume and therefore lower cost.

Operational control of contact stabilization process

Abstract A model for Contact‐Stabilization process is developed. Operational strategies to control the process is discussed. It is apparent that the MLSS distribution is very important if a stable operation and high efficiency is desired.

Early Mother-Infant Contact and Infant Temperature Stabilization

Thirty-four healthy mother-infant dyads were divided into two groups to determine the effect of postdelivery skin-to-skin contact on infant temperature stabilization. Nineteen control infants were placed in heated cribs, while 15 study infants were given immediate and extended physical contract with their mothers. Axillary and rectal temperatures were measured five minutes after birth and one hour after the infants left the delivery room. The results indicate that separating normal newborns from their mothers for the purpose of stabilizing temperature may not be necessary.

The activated sludge process part 2. Application of the general kinetic model to the contact stabilization process

The general aerobic activated sludge model including nitrification for processes treating principally municipal wastewater is applied to the contact stabilization process treating municipal wastewaters. The application involves two changes to the model: (i) a change in one of the values of the kinetic constants in the expressions of the substrate utilization rates; (ii) a change in the enmeshment mechanism by accepting that a fraction of the particulate COD which is not adsorbed onto the active organisms, does not become enmeshed in the sludge flocs and escapes with the effluent. Accepting only these changes it was found possible to satisfactorily simulate the behaviour of the contact and stabilization reactors of the process under both constant and cyclic conditions of loading. For design, the general activated sludge model, as applied to the contact stabilization process, requires the process, configuration to be completely specified. To aid in the initial design of the process, a preliminary design procedure is presented by means of which the volumes, sludge concentrations and retention times of the contact and stabilization reactors may be determined from five independent parameters which are assumed to govern the process. These are the sludge age, recycle ratio, fractional distribution of the sludge mass between contact and stabilization reactors, daily COD mass load and the average sludge concentration in the process.

Secondary Treatment Alternatives: Suspended Growth

The modifications of conventional activated sludge capable of producing secondary effluent when followed by properly designed sedimentation units include extended aeration, oxidation ditches, pure oxygen activated sludge, contact stabilization, and step aeration. The activated biofilter process, which combines a trickling filter with an aeration basin, can be classified as a suspended growth system due to the nature of the solids produced. Classification of activated sludge processes is most easily done according to operational characteristics such as aeration time, food-to-microorganism ratio, mixed liquor solids concentration, and mean cell-residence time. The modified Monod model is the most general of several reaction rate models currently being used for design. The selection of alternatives necessitates assessment of the constraints and tradeoffs of each process from a technical viewpoint. As well, other factors such as performance, cost effectiveness, energy utilization, and local environmental and social considerations must be evaluated during the decision-making process.

Activated Sludge Process Modification Study

A laboratory study was conducted with a colloidal wastewater that was fed to model completely mixed and contact stabilization units. The units were operated at steady-state conditions at several mean cell residence time values. Using mean cell residence time as a basis for comparison it was determined that the cell yield coefficient and microorganism decay coefficient were similar for the two systems and that waste treatment efficiency was also similar. From these results it was determined there is no difference in the kinetics or operational performance between these two modifications to the activated sludge process.

Mathematical models of biological waste treatment processes for the design of aeration tanks

The paper discusses the application of formal mathematical models of biological treatment in designing aeration tanks. It deals with a complete mixing aeration tank, an ideal plug-flow tank, and a many-step aeration tank. Selection is substantiated of the simplest non-linear Monod's model for biochemical oxidation. A new model is advanced taking into consideration, among others the effect of pollutant sorption by activated sludge. The model permits calculating the optimal volumes of the aeration tank and stabilization tank in the contact stabilization system.

New Approach to Bacterial Kinetics in Wastewater

A mathematical model for bacterial growth is developed by consideration of the analogy between bacterial growth and a nonelementary chemical reaction. The resulting model is very general, including both substrate storage and basal metabolism. Under certain defined conditions it reduces to the known Monod-type and two-phase growth models. It predicts quantitatively the large substrate uptake rates seen in the contact stabilization process. In this model the concentrations of substrate and biomass are defined in terms of their carbon content as this approach gives greater conceptual and practical simplicity than conventional approaches based on BOD, COD, VSS, etc. Predictions of the model are found to agree with experimental data from a system of mixed denitrifying bacteria metabolizing a dilute dextrose substrate.

The contact stabilization activated sludge process—oxygen utilization, sludge production and efficiency

A kinetic model of the contact stabilization process has been developed and experimentally verified with the aid of bench-scale activated sludge units treating domestic sewage. The model provides information on the relationship between the design parameters (process loading, temperature, residence time distribution) and process performance (sludge, production, oxygen uptake, COD-removal, organic nitrogen conversion, nitrification and effluent suspended solids). An oxygen equivalence mass balance equation, which is applicable to all activated sludge process modifications is proposed and may be used in the design and operation of these processes.