Wastewater Treatment Units Research Articles

Recycling of Al-rich industrial sludge in refractory ceramic pressed bodies

Processing of mullite-based refractory ceramic bodies by unidirectional dry pressing, from different formulations that include Al-rich sludge, as single or main component is described. The sludge is produced from anodising or surface coating processes and is generated in the wastewater treatment unit of an industrial plant. After a detailed characterisation study, involving determinations of chemical, thermal and granulometric parameters, as-received, and previously dried (110 °C) or calcined (1400 °C) sludge was used alone or combined with common ceramic raw materials, such as diatomite, kaolin or ball clay. Green bodies were consolidated by dry pressing and fired at temperatures in the range 1400–1650 °C, and the mechanical, thermal and electrical properties of the fired products were evaluated. Promising refractory materials based on mullite, mullite+alumina, or alumina were obtained.

Integration of biotechnological wastewater treatment units in textile finishing factories: from end of the pipe solutions to combined production and wastewater treatment units

Increasing costs for water, wastewater and energy put pressure on textile finishing plants to increase the efficiency of wet processing. An improved water management can decrease the use of these resources and is a prerequisite for the integration of an efficient, anaerobic on-site pretreatment of effluents that will further cut wastewater costs. A two-phase anaerobic treatment is proposed, and successful laboratory experiments with model effluents from the cotton finishing industry are reported. The chemical oxygen demand of this wastewater was reduced by over 88% at retention times of 1 day or longer. The next step to boost the efficiency is to combine the production and wastewater treatment. The example of cotton fabric desizing (removing size from the fabric) illustrates how this final step of integration uses the acidic phase bioreactor as a part of the production and allows to close the water cycle of the system.

A study of the effect of isothiazolones on the performance and characteristics of a laboratory-scale rotating biological contactor.

To study the effect of the isothiazolone biocide (Kathon WT) on the performance of laboratory-scale rotating biological contactors (RBCs) and their component biofilms. Biofilms were established on the RBCs and then exposed to 0.7-15 p.p.m. isothiazolones. Young, 1-week-old, biofilms were found to attain treatment efficiency equal to that of mature, 2-month-old, biofilms. Isothiazolone concentrations at 3 p.p.m. and above caused a progressive decline in treatment efficiency and 15 p.p.m. isothiazolones inhibited all microbial activity and resulted in the death of the biofilms. Bio-oxidation and the biodegradation of isothiazolones within the biofilms ontinued unhindered at concentrations which caused the total inhibition of planktonic bacteria. There was at least a 10-fold difference in susceptibility of planktonic and biofilm bacteria to isothiazolones. The chemical oxygen demand (COD) test was shown to be a reliable tool for investigating the efficiency of wastewater treatment units when the influent contains isothiazolones, while the biochemical oxygen demand (BOD) was unreliable due to the inhibition of bio-oxidation by the biocide. The results show that RBCs can be used to treat effluents containing isothiazolones at concentrations up to 1.5 p.p.m.

Assessment of Automobile Industry Wastewater Treatment Units

Assessment of Automobile Industry Wastewater Treatment Units

Duckweed based wastewater treatment (DWWT): design guidelines for hot climates

Conventional wastewater treatment systems are expensive in either investment or running costs. On the other hand, waste stabilisation ponds may be unable to meet effluent standards for nutrients. Wastewater treatment using duckweed therefore becomes more significant as an option capable of achieving effluent standards and generating revenue from selling the duckweed. However existing duckweed based wastewater treatment (DWWT) systems have high land requirements despite being able to reduce concentrations of organic compounds and pathogens to acceptable levels. Improved guidelines for the design of DWWT are necessary to obtain a reliable and cost-effective wastewater treatment plant using duckweed. This guideline provides a DWWT design program using spreadsheets for different configurations of wastewater treatment units using duckweed. The design program developed suggests that a combination of anaerobic ponds, DWWT systems and maturation ponds can minimise land requirements and capital costs while achieving specified effluent standards. In order to achieve effluent standards, the land required is typically from 1.5 to 1.8 m2/capita (excluding associated facilities), capital costs are in the range from 7.9 to 9.7 USD/capita, with a retention time from 15 to 18 days. Income generation is dependent mainly on the social and cultural acceptability of duckweed use within the community.

Assessment of automobile industry wastewater treatment units.

Assessment of automobile industry wastewater treatment units.

Heavy metal removal in waste stabilisation ponds and high rate ponds

Heavy metals, zinc (Zn), copper (Cu) and lead (Pb) removal in two wastewater treatment units were compared. One of the systems consisted of a train of Waste Stabilisation Ponds (WSP) including one anaerobic, three facultative in series and two maturation ponds, also in series. The other system, called High Rate Ponds (HRP) consisted of one anaerobic, one High Rate Algal Pond (HRAP) and two maturation ponds in series. The two treatment systems were located on the same site and received the same wastewater. Data collected from the two treatment systems, for a period of three consecutive months (May, June and July, 1995) show that the content of the three elements in the crude wastewater of the city of Ouarzazate varied from 210 to 340 mg/l for Zn; 35 to 55 for Cu and 30 to 25 for Pb. The removal rate for the three elements reached 91, 92 and 71% respectively for Zn, Cu and Pb in the WSP train. The corresponding values in the HRP train were, respectively 89, 88 and 51%. However, since the two trainswere not receiving the same flow, the use of specific removal rate expressed as mg removed m-2 d-1 showed that the HRAP was 1.3, 10 and 2 times more efficient respectively for Zn, Cu and Pb removal than the three facultative ponds in series of the WSP. Also, the collected data showed that the content of the sediment of the anaerobic pond was high for all the three elements. However, the recorded concentrations 613, 99 and 78 mg/kg, respectively for Zn, Cu and Pb did not exceed the EEC recommended limits.

Impact of Chromium and Copper on Fixed-Film Biological Systems

A laboratory investigation was performed to study the recovery of a biological tower (fixed-film biological wastewater treatment unit) after dosing the influent with copper or chromium. The pilot-scale biotower (1.83 m high) was shocked with copper at three different influent concentrations (3, 56, and 47 mg/L). A continuous 3 mg/L dose had no significant impact on soluble 5-day biochemical oxygen demand removal performance. After slug doses of 56 or 57 mg/L for 10 h, the biotower established a new steady-state condition, in terms of soluble 5-day biochemical oxygen demand in the effluent, within 14 h. Recoveries from shock loads of chromium were slower: Recovery from doses of 9 mg/L of chromium occurred after 12 h, but recovery from doses of 38 and 96 mg/L required approximately 250 h. The metals concentrations in both biofilm and effluent were described by a power function with a concentration equal to a constant multiplied by time to a power. Uptake of chromium was determined to be nearly independent of dose, at the doses tested.

Degradation of morpholine by an environmental Mycobacterium strain involves a cytochrome P-450.

A Mycobacterium strain (RP1) was isolated from a contaminated activated sludge collected in a wastewater treatment unit of a chemical plant. It was capable of utilizing morpholine and other heterocyclic compounds, such as pyrrolidine and piperidine, as the sole source of carbon, nitrogen, and energy. The use of in situ 1H nuclear magnetic resonance (1H NMR) spectroscopy allowed the determination of two intermediates in the biodegradative pathway, 2-(2-aminoethoxy)acetate and glycolate. The inhibitory effects of metyrapone on the degradative abilities of strain RP1 indicated the involvement of a cytochrome P-450 in the biodegradation of morpholine. This observation was confirmed by spectrophotometric analysis and 1H NMR. Reduced cell extracts from morpholine-grown cultures, but not succinate-grown cultures, gave rise to a carbon monoxide difference spectrum with a peak near 450 nm, which indicated the presence of a soluble cytochrome P-450. 1H NMR allowed the direct analysis of the incubation medium containing metyrapone, a specific inhibitor of cytochrome P-450. The inhibition of morpholine degradation was dependent on the morpholine/metyrapone ratio. The heme-containing monooxygenase was also detected in pyrrolidine- and piperidine-grown cultures. The abilities of different compounds to support strain growth or the induction of a soluble cytochrome P-450 were assayed. The results suggest that this enzyme catalyzes the cleavage of the C-N bond of the morpholine ring.

Comparison of the cost of the pressurized wastewater treatment process with other established treatment processes

A biological wastewater treatment unit under the influence of pressure was operated at pressures of up to 6 bar. It was demonstrated the capability of operating effectively with high carbonaceous oxidation and nitrification efficiencies at loadings of up to 13 g BOD m −2 day. Another advantage of the pressurized treatment unit was observed to be its low sludge production. The cost of the pressurized treatment unit has, however, become an important factor for the applicability of the pressurized treatment unit. An investigation was carried out to determine the approximate cost of a proposed full-scale pressurized unit. The comparison between the pressurized unit and the established treatment processes were made for three populations of 500, 1000 and 3000 persons. The costs were then compared with those of various other conventional biological treatment processes capable of treating an equivalent wastewater load. The conventional processes selected for comparison were the activated sludge, biological filtration and conventional RBC. The sludge disposal cost for the pressurized unit was appreciably lower than that for the other processes. The results indicated that the cost of the pressurized unit (present value for a 20-yr period) and the costs of the activated sludge and conventional RBC processes were found to be similar for the smaller populations. However, a substantial saving could be obtained with the pressurized unit for the larger populations. In addition, there was an indication that the land requirement of the pressurized treatment unit decreased appreciably as the flow rate increased.

Implementation of an alternative skimming system and improvement of the final effluent quality in API separators.

This article present and analyzes a series of pilot plant test results of a system far oplimizing !he efficiency of API type separators in the recovery of crude oils and light hydrocarbons (fuel oíl) from wastewater. The system consists of two phases: the first being a new skimming device, as an alternative lo the traditional slotted pipe skimmer, that employs an oleofilic bond. In the second phase the quality of the separator effluent is improved by using natural adsorbent filters based on vegetal fibers. Four types of fibers were chosen: fique, water hyacinth, sáwdust, and pineapple leave fiber. The skimmer is operated by means of a neumatic engine that spins a series of rollers which serve as support far an oleofilic bond. As the bond rotates, it removes by adherence the hydrocarbon floating in the water. During the experimental phase the variables were: type of bond material, velocity of bond rotation and angle of bond inclination with regard to that of the water surface. According to the results of the different tests the experimental system is effective in removing floating hydrocarbons, in the form of crude oil or as a refined product, from an aqueous media. The system can easily be adapted to oily wastewater treatment units, existing or projected.

Stormwater management in industrial facilities: An integrated approach

AbstractNumerous existing and proposed regulations have forced owners/operators of industrial facilities to reevaluate current methods for management of stormwater which falls within the confines of their facilities. Most have found it necessary to integrate their current stormwater and wastewater management practices into a comprehensive environmental compliance program. The development of an integrated stormwater management program should focus on the following objectives: compliance with state and federal regulations. the minimization of the volume of stormwater requiring treatment. the minimization of the impacts on process/production unit operations the minimization of the impacts on wastewater treatment unit operations. A well designed and properly implemented stormwater management program can reduce capital and operating costs and enhance effluent quality.

Wastewater Treatment Optimization Model for Developing World. II: Model Testing

This paper describes the testing of a wastewater treatment optimization model for the developing world (described by Ellis and Tang in 1991) in applications to four existing wastewater treatment units in Puchong, Malaysia; Shatin, Hong Kong; Min shen, Taiwan; and Pattaya, Thailand). In each case, a reciprocal matrix of a suitable number of wastewater-treatment alternatives (decision variables) was developed for each of 20 technical and socio-economic parameters. These 20 parameters are flow capacity, influent and effluent characteristics, size of treatment site, nature of site, land cost for site, local/foreign money for construction, local skill for construction, community support, power source, availability of local material, cost of operation and maintenance, professional/technical skill available for operation and maintenance, administration set up, training, professional ethics, climate, waterborne diseases, and endemic vector-borne diseases. The matrices were then integrated by a computer program to obtain a final ranking of the original alternatives using the analytic hierarchy process mathematical technique. The model was also tested for its sensitivity in predicting changes to an appropriate technology selected as socio-economic parameters change with time.

Removal of chromium, copper and nickel by water hyacinth(eichhornia crassipes)part ii: Industrial application

Heavy metals were analyzed in various samples of waste water from a metal plating factory in Istanbul. Chromium, copper and nickel uptake from industrial wastewater by water hyacinth (Eichhornia crassipes) at different dilution was examined by AAS and UV‐visible spectrophotometric methods. The results were statistically compared by t‐ ad F‐ tests. Since heavy metals are effectively removed, water hyacinth may be used for wastewater purification after dilution or as a step of wastewater treatment unit for industrial effluents under conditions in Turkey.

Performance of membrane separation bioreactor at various temperatures for domestic wastewater treatment

The effect of a short term temperature change on organic carbon oxidation, nitrogen removal and membrane permeate flux in a membrane separation bioreactor was studied. The process was developed as a household wastewater treatment unit, employing direct immersion of hollow fiber membrane modules for solid-liquid separation in an activated sludge aeration tank. The organic carbon oxidation in the system was not deteriorated by a short term temperature change whereas nitrogen removal decreased significantly as the temperature dropped to 10°C. Reduction in the percentage of strict aerobic bacteria suggests that limitation of oxygen transfer probably resulted in the decrease of the amount of nitrifying bacteria and, thus, inhibition of nitrification at low temperature. A temperature decrease affected the permeate flux not only by increasing the viscosity of mixed liquor but also changing the properties of the cake layer, i.e. cake layer thickness and/or porosity. An hysteretic curve of gel and cake layer was used to show the effect of temperature changes on the resistance of gel and cake layer. By differentiating the resistances of the porous cake layer from those of the gel and the extracellular matrix, changes in the cake layer thickness and/or porosity of the cake layer could be used to explain the changes in the cake layer resistance.

Dynamic simulation of submerged packed biofilters in wastewater treatment plants

This study reports on the use of dynamic simulation for wastewater treatment units involving submerged packed biofilters. It enlights different aspects of the dynamic modelling of such non conventional systems (biological reaction scheme, …) and the numerical strategy used to solve the resulting set of Partial Differential Algebraic equations (PDAE). Illustrative applications in the case of denitrification and denitritation with pilot plant data comparison sketch the interest of dynamic simulation.

Removal Efficiencies of Microorganisms in Wastewater Treatment Processes

The removal characteristics of indigenous microorganisms in wastewater treatment unit processes were studied at five operating wastewater treatment plants. The removal efficiencies of the selected microorganisms in each unit process were dependent upon not only the systems but also the kinds of microorganisms. In almost all processes, the removal efficiencies of total coliforms were similar to or higher than those of Clostridium perfringens except for filtration processes. In the additional survey, focussed on the comparison of removal efficiencies of total coliforms, Cl. perfringens and coliphages, little difference was found between CL perfringens and coliphages. From these results, it may be suggested that CL Perfringens is an effective indicator microorganism for evaluating microorganism removal in wastewater treatment processes and systems.

Analysis of Techniques for Evaluating and Optimizing Existing Full-Scale Wastewater Treatment Plants

This paper presents an analysis of techniques applied to the evaluation and optimization of nearly 40 full-scale wastewater treatment plants. The techniques evaluated included oxygen transfer analysis by off-gas and hydrogen peroxide techniques, clarifier analysis by stress testing and hydraulic analysis, on-line monitoring, and reactor tracer testing. The results indicate that the process performance of full-scale wastewater treatment units can be measured using these techniques. Advantages exist for off-gas testing when applied to the analysis of low to moderate turbulence diffused air systems. Hydrogen peroxide analysis can be applied to essentially all oxygen transfer systems. Stress testing can be used to quantify the treatment capability of clarifier units; hydraulic analysis can then be used to identify clarifier upgrade opportunities and to quantify the impact of any modifications implemented. On-line monitoring is the most powerful technique tested. It has been used successfully to optimize and improve full-scale treatment plants. Reactor tracer testing can be used to identify upgrade opportunities for full-scale units.

Variability of effluent quality in a multi-step complex for wastewater treatment and storage

The present paper deals with the variability of efluent quality in a complex for wastewater treatment and storage. The complex is made up of several steps: a treatment plant followed by a two-cell stabilization reservoir and an operational reservoir in series. The generally held notion that wastewater treatment units reduce inflow quality variability stem from the wrong use of standard deviation to compare data of different magnitude. The standard deviation is a statistic that describes the variability of data in absolute terms. It is not appropriate to compare outflow and inflow quality variability in a treatment plant, since outflow quality values are usually several times lower than inflow ones. The same problem arises when comparing different parameters (e.g. the variability of pH with the variability of BOD). In these cases it is necessary to describe the variability of data in relative terms. The coefficient of variation (CV) is used in this work to describe the variability of each single quality parameter at each step of the Kishon complex. There are conspicuous differences in variability between the wastewater quality parameters. These differences can help for a better selection of parameters for both monitoring and modelling purposes, as well as for determination of differential sampling frequencies in monitoring programs. The different steps of the treatment complex hardly differ in the variability of effluent quality as a whole, expressed as the average CV of all parameters in each step. Wastewater quality variability is only partially transmitted along the complex, but local born disturbance maintains the total amount of variability at each step almost unchanged. Control and reduction of variability at one step of the complex will not significantly affect the amount of variability in the subsequent steps.

A review of pilot-scale studies of bottom and surface velocities within air-agitated circular and rectangular vessels

The use of bottom or surface fluid velocity within air-agitated circular and rectangular vessels has been studied as a possible design parameter to achieve a specified scale of agitation. Experimental data are presented in terms of five dimensionless numbers involving the fluid velocity, the depth of fluid in the vessel, the elevation of the diffuser above the vessel floor, the air flow rate, and the compressor power required. Design equations are obtained for a total of 506 physical observations with a ring diffuser around the perimeter of a circular vessel, a pipe diffuser at the centre of a circular vessel, and a line diffuser at the centre line or end wall of a rectangular vessel. The applicable range of variables for each equation is provided. It is shown that both bottom and surface velocities increase with an increase in air flow rate or compressor power requirement for a specified fluid depth. For a constant air flow rate and fluid depth, the surface velocity always exceeded the bottom velocity. The surface and bottom velocities are related to operating conditions in different water and wastewater treatment units in which a specified degree of uniformity of the vessel contents has to be maintained in order to keep a specified particle in suspension. The sensitivity analysis of the model revealed that the fluid depth was the most important design parameter in controlling the velocities within air-agitated vessels. Key words: bottom velocity, surface velocity, velocity gradient, degree of uniformity, air-agitated rectangular vessels, air-agitated circular vessels.