Monitorizarea Parametrilor Din SEAU

8/12/2019 Monitorizarea Parametrilor Din SEAU

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Monitorizarea parametrilordin SEAU

Constantin Mihai-Valentin

MB1

Anul 2


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Water Authorities and municipalities are governed by national or local regulations onthe quality of water they discharge, so effluent from industrial and domestic use must becleaned and treated prior to release to the environment. The treatment plant shouldtherefore remove any materials that are likely to be harmful to the environment, ranging

from large objects (cans, wood and debris) to suspended solids, floating material suchas fat and even dissolved substances. Consequently a range of treatment is required toremove all these contaminants. In order to operate the plant correctly and efficiently,measurements of the main parameters are required. These usually include:

1. Flow and level2. pH, conductivity and turbidity3. Pressure and temperature *4. Water analysis parameters (DO, P, NH

4, NO

3etc.)

A typical treatment process is shown in figure 1. The dotted lines show discrete parts ofthe overall process, so that a generic 4-step process can be listed for both the waterside and solids handling as:

Module A: The influent line and associated processesModule B: First stage mechanical separation primary clarificationModule C Effluent discharge chemical treatment and disinfection processesModule D: Biological degradation nitrification/denitrification breakdown of influentsolidsModule E: Sludge blending and thickening mixing of raw and waste activated solidsModule F: Digestion processes final breakdown of solids by bacterial meansModule G; Dewatering process removal of excess fluid and solids optimisationModule H: Solids disposal


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In the upper half of the process diagram (figure 1), the first stage consists of the influent

lines, pump station and plant intake (section A), where coarse screens remove largeobjects. Sometimes smaller screens (1-2cm) are used to remove floating fat, paper andsmaller items such as fruit, rind or waste food lumps. The liquid then passes into the

primary clarifiers (Section B) where suspended solids and floating substances areremoved. The raw liquid passes to the biological treatment tanks (section D) and theprimary sludge goes to the thickener (section E) for blending.In the aeration tanks, bacteria feed on the organic matter and nitrify harmful ammonia.

Artificial oxygenation promotes this process so the bacteria multiply and accelerate thewater cleaning process. The partly-cleaned liquor is fed to the secondary clarifier wherefurther separation occurs. The activated sludge in the bottom of the secondary tanks ispassed to the thickening tank (section E) for blending with the sludge from the primaryclarifiers. The relatively clean liquid from the top of the secondary clarifier is thenchlorinated and de-chlorinated prior to discharge (section C). In some more advancedplants, a chemical cleaning process is added to the biological process . These may use

precipitants such as ferric chloride or aluminum sulphate to remove organic carbon,phosphorus and some of the nitrogen based compounds. This may occur in either theprimary or secondary clarifiers or in the aeration tank.

The lower half of figure 1 shows solids handling and disposal. Sludge from the primaryand secondary clarifiers is mixed. The thickened sludge passes to the digester (sectionE) where further biological process generates methane gas, which is often used as anenergy source. The digested sludge from the base of the digester then passes to thedewatering stage, (section G) where a variety of techniques are used to remove most ofthe water and produce an energy-rich residue. This residue is pumped to the disposalarea (section H) to be used for incineration, for fertilizer production or for landfill,depending on the chemical composition of the treated residue.

Inlet Measurements

Measurements at the plant inlet are usually mandatory help monitor the incomingpollution load and to satisfy the design parameters of the plant are not exceeded. Themost important measurements are flow quantity, pH, temperature, conductivity and thebiological oxygen demand (BOD).

A measurement of pH at several points in the inlet area is required to ensure efficientplant operation and to monitor the effect of the influent water on the concrete structures

and channels. This measurement is often made alongside a temperature sensor forsimilar reasons. A low pH value often induces damage in pipes, valves and othermetallic components. Conductivity is often not measured at the inlet but is useful to helpmonitor salt content and other materials that affect pH and temperature measurement.Some chemical addition at inlet may be required to keep the influent within the range pH6 8.5. The BOD figure is used to gauge the amount of oxygen required by the microbacteria to break down organics and other waste present. A high BOD means that largeamounts of air or oxygen will be needed to affect the solids breakdown. Sometimes


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sampling systems are also used the help determine the plant loading and report onremoval efficiency when compared to effluent samples.

Level measurements are common in the pumping station and in the coarse screens toensure that the plant operates within capacity and that the bar screens do not becomeclogged or damaged. One of the most important measurements on the entire plant isthe accurate measurement of flow at the main pump station inlet. This signal is fed toother parts of the plant as part of the control signal. Errors in metering here may affectthe entire efficient operation of the plant.

Primary clarifier

Two possible process variations are possible, the basic process being just a simple inlet

to each clarifier basin and the more enhanced variation of flocculent addition in theclarifier inlet line. Whatever the process variant, the vessel bottom is usually extendedto allow sludge to collect for efficient draw-off. It is important that sludge level andquantity of the suspended solids is measured. Both these parameters act as controlinputs to the clarifier dump valve that allows the primary sludge to be pumped to thethickener. Turbidity and flow measurement of the outlet liquor to the biological treatmenttanks are important and sometimes samplers are additionally used to ensure a richliquor for treatment. The purpose of flocculent dosing is used at the clarifier inlet toseparate light and heavy solids particles.

Aeration tank

In normal practice, oxygen is measured and regulated in the aeration tanks, but controlof the return sludge or return water flow less common. The essential measurementstherefore in the aeration tank are dissolved oxygen content and pH. This part of theprocess can more effcienttly be control using a combination of an ammonia monitor anda DO sensor.

Secondary clarifier

It is important to keep a fixed level of sludge in the base of the clarifier to ensure theavailability of biomass in the system for recirculation to the aeration tank and maintainits concentration within acceptable limits. Sludge discharge is either continuously orintermittently made from the base of the clarifier, passing into the pre-thickener andsludge blender. Suspended solids level (and even concentration profile) measurement


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ensures an effective separation takes place in the clarifier. In order to monitor thequality of water in the overflow channels, turbidity should be monitored.

Bibliography:

1. http://www.ewa-online.eu/tl_files/_media/content/documents_pdf/Publications/E-WAter/documents/5_Haimi_Mulas_Vahala_Process_Automation_051010.pdf

2. http://www.automationworld.com/process-automation/water-wastewater

3. http://www.pump-zone.com/topics/instrumentationcontrols/automation-and-control-systems-wastewater-treatment-plants

4. http://www.endress.com/eh/home.nsf/#page/id/3D211D6AC9A1D995C125793E003C6ABD
http://www.ewa-online.eu/tl_files/_media/content/documents_pdf/Publications/E-WAter/documents/5_Haimi_Mulas_Vahala_Process_Automation_051010.pdfhttp://www.ewa-online.eu/tl_files/_media/content/documents_pdf/Publications/E-WAter/documents/5_Haimi_Mulas_Vahala_Process_Automation_051010.pdfhttp://www.automationworld.com/process-automation/water-wastewaterhttp://www.pump-zone.com/topics/instrumentationcontrols/automation-and-control-systems-wastewater-treatment-plantshttp://www.pump-zone.com/topics/instrumentationcontrols/automation-and-control-systems-wastewater-treatment-plantshttp://www.endress.com/eh/home.nsf/#page/id/3D211D6AC9A1D995C125793E003C6ABDhttp://www.endress.com/eh/home.nsf/#page/id/3D211D6AC9A1D995C125793E003C6ABDhttp://www.endress.com/eh/home.nsf/#page/id/3D211D6AC9A1D995C125793E003C6ABDhttp://www.endress.com/eh/home.nsf/#page/id/3D211D6AC9A1D995C125793E003C6ABDhttp://www.pump-zone.com/topics/instrumentationcontrols/automation-and-control-systems-wastewater-treatment-plantshttp://www.pump-zone.com/topics/instrumentationcontrols/automation-and-control-systems-wastewater-treatment-plantshttp://www.automationworld.com/process-automation/water-wastewaterhttp://www.ewa-online.eu/tl_files/_media/content/documents_pdf/Publications/E-WAter/documents/5_Haimi_Mulas_Vahala_Process_Automation_051010.pdfhttp://www.ewa-online.eu/tl_files/_media/content/documents_pdf/Publications/E-WAter/documents/5_Haimi_Mulas_Vahala_Process_Automation_051010.pdf

Monitorizarea Parametrilor Din SEAU

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