A.V. Romashko - 1, I.Iu. Boiko - 2, E.R. Marykin - 3 et al - 4.
Key words: automated process control system (APCS), software and hardware system (SHS), local control station, physicochemical treatment, flotation, biological treatment, sludge treatment.
Objective of the works described in this paper and performed by the engineering company MY PROJECT, was the design and commissioning of automated local wastewater treatment plant (LWWTP) of three poultry farms: Agro Plus LLC (Izobilny, Stavropol Region), Kaluzhskaya Poultry Farm JSC (PRODO group, Kaluga region) and Tambov Turkey LLC (Cherkizovo group, Tambov region).
The modern requirements for the operation of a wastewater treatment plant include: 1) reducing operating costs for industrial wastewater treatment; and 2) the possibility of a non-permanent presence of maintenance personnel.
The need for automation of a wastewater treatment plant was described by scientists in the 60-70s of the XX century, and was presented as a mandatory standard in SNiP II-32-74 . Since then, automated process control systems (APCS) have been developed with leaps and bounds, and the modern local wastewater treatment plants for the treatment of wastewater from food enterprises are hardly conceivable without automated process control systems or at least without local automation units.
The use of automation systems eliminates such drawbacks as fatigue of maintenance personnel, its subjectivity in assessing emerging situations, limited response rate to sharp changes in operating parameters , reduces operating costs, including staff salaries, and minimizes the consequences of emergencies etc.
This paper deals with the experience of MY PROJECT in the design and implementation of the automation of the wastewater treatment plant for the meat industry examplified on Agro-Plus LLC, Kaluzhskaya Poultry Farm JSC and Tambov Turkey LLC.
The application of the process control system at the three facilities listed above makes it possible to simplify the operation of the wastewater treatment plant and reduce the operating costs for their maintenance.
The management of Agro-Plus LLC poultry farm in 2016 assigned the specialists of MY PROJECT JSC to implement local wastewater treatment plant “on a turn-key basis” subject to minimum necessary time for the LWWTP maintenance, as well as reduced operating costs through the use of software and hardware control system.
Industrial wastewater in the amount of 900 m3/day flow by gravity to the wastewater pump station (WWPS), where they are pumped with the pumps into the building of mechanical and physico-chemical treatment of industrial wastewater.
The process of wastewater treatment consists of the following process units:
Mechanical treatment of industrial wastewater is carried out on a screw screen with a 2.0 mm clearance. The screw screens trap mechanical debris of more than 2 mm. The detained and dehydrated wastes are collected in the hopper and discharged with the sluice gate into the container and then removed for disposal.
After the screens, mechanically treated industrial wastewater is fed by gravity for equalization to smooth out the peak wastewater inflows, both in terms of consumption and in terms of chemical composition. To prevent precipitation of suspended and mineral particles, a mechanical mixer is installed in the equalization unit. Mixer works either by timer and at reaching a predetermined level.
Wastewater is supplied to the induced air flotation unit by submersible pumps installed in the mixer. The pumps are switched on and off when the preset water level is reached in the equalization unit. To measure the wastewater level in the equalization unit, a level gauge is provided, which is used to determine the degree of filling of the equalization unit and to control the operation of the mixers and feed pumps.
Display of the level gauge readings and the control of the pumps and mixers installed in the equalization unit are provided from the control cabinet of the induced air flotation unit.
Physico-chemical treatment by induced air reagent flotation. Mechanically treated industrial wastewater are pumped out from the equalization unit into the tubular flocculator. The flocculator is equipped with samplers for sampling the floater incoming wastewater, as well as for monitoring the set doses of reagents.
The following introduction sequence of chemical reagents is provided:
Undissolved contaminants were removed from wastewater using an induced air pressure reagent flotation unit developed by the specialists of MY PROJECT JSC based on the unique MY DAF technology. A general view of the physico-chemical treatment shop is shown in Figure 1.
Air dissolution in water occurs in a saturator. Air is supplied to the saturator from the compressor. Part of the water clarified in the floater is taken out by a recirculation pump and fed to a saturator where an effective dissolution of air in the water is achieved, after which the air-saturated water is mixed with the industrial wastewater passed through the flocculator for separation in the induced air flotation unit.
The flotation foam is collected from the floater surface by scrapers into a pocket for the flotation foam. To pump the flotation foam from the collection pocket, a screw pump is provided. The flotation foam is pumped to the sedimentation tank.
A foam pump operates intermittently from a two-contact electrode level gauge installed in the foam collection pocket.
During the treatment of wastewater in the lower part of the floater, a sediment forms. For the removal of the sediment, a shut-off valve with a pneumatic drive is installed. The sludge removal valve operates in timer mode. Sediment from the floater due to hydrostatic pressure moves to a horizontal sand trap, where heavy mineral impurities precipitate. Clarified water is supplied further to the equalization unit.
To intensify the flotation process, the solution of the coagulant and flocculant is dosed into the water being purified, and the solution of sodium hydroxide is used for pH adjustment.
During the commissioning, the following reagents were used as the coagulant:
Based on the results of the technical and economic analysis, 40% ferric chloride solution is recommended as a coagulant, which has a lower purchase price than Aqua-Auratt18. The dosage of the coagulant solution is provided from an IBC container.
To feed the coagulant solution into the flocculator, diaphragm dosing pumps with manual flow control are used.
To adjust the wastewater pH, a solution of sodium hydroxide is used. For dosing sodium hydroxide solution, a diaphragm dosing pump with automatic flow control is used. The dosage of the sodium hydroxide solution is from the IBC container to the dosing point in the flocculator. The supply of sodium hydroxide solution is automatically performed according to the pH of the incoming wastewater, however, manual alkali supply to the flocculant is possible, when the operator independently adjusts the capacity of the alkali dosing pump.
During commissioning, a solution of commercial NaOH with a sodium hydroxide concentration of 40% was used, the calculated concentration of the working solution of alkali after dilution was 8%. The consumption of 8% alkali solution was 3.75-7.5 l/h. It is possible to dose sodium hydroxide solution both automatically according to pH and manually. It is also possible to disable the alkali dosing pump due to acceptable pH values after flotation.
The flocculant solution preparation and dosing unit consists of a station for the preparation of a flocculant solution and a screw dosing pump for a flocculant solution. The dry flocculent is filled up by the operator into the flocculant funnel of the station. To prepare the flocculant solution, the station is fed with water from a pressurization station powered from the jet break tank. By means of dosing pumps, the flocculant solution is fed to the dosing station in the flocculator.
The treated industrial wastewater after physico-chemical treatment in the induced air flotation unit enters the well of the treated wastewater discharge system and is discharged into the municipal sewer.
The control of all process equipment of the local wastewater treatment plant is provided from the touch control panel of the flotation control cabinet with the help of the software and hardware system developed by MY PROJECT JSC.
The software and hardware system (SHS) for controlling a set of process equipment for physico-chemical treatment of industrial wastewater at AGRO-PLUS LLC based on a flotation unit with the use of the unique MY DAF technology is designed for automated control and regulation of the main process parameters of the plant for providing remote automated process control, for automatic registration of process parameters, recording of the operator’s action and events.
SHS provides for:
The visualized information is displayed to the operator on the control panel of the control cabinet of the induced air flotation unit and the local control panel. The general view of the Flotation mimic diagram on the control panel is shown in Figure 2.
The operator of wastewater treatment plant has the following remote control capabilities when working with the touch panel:
Figure 2 - Flotation touch panel mimic diagram
The illustrated mimic diagram graphically displays a status of:
The application of the industrial process automation system for wastewater treatment made it possible to simplify the operation of the treatment plant and to reduce the amount of electricity consumed, including through the mixer's intermittent operation instead of constant mode. Based on the results of the implementation of this project, AGRO-PLUS LLC gave positive feedback on the local wastewater treatment plant.
Design works on the reconstruction of wastewater biological treatment plant were carried out by Ecopolymer-M CJSC (currently – MY PROJECT JSC) in 2013-2014. A positive opinion of the state examination of Kaluga region was issued in August 2014. At present, construction and installation works and supply of process equipment have been completed, commissioning is in progress.
Wastewater entering the wastewater treatment plant of Kaluzhskaya Poultry Farm JSC in the amount of 5500 m3/day, undergoes mechanical treatment, biological treatment, post-treatment through the sand filters and disinfection, and then discharged to the fish farm. Sludge treatment is provided mechanically with the screw thickeners and belt filter presses.
Description of the operation of wastewater biological treatment plant and the treatment of raw sludge and excess biological sludge is of special interest for this paper.
Biological treatment procedure description. The process of re-engineering of existing wastewater biological treatment plant provides for the implementation of the nitri-denitrification technology according to the Ludzack-Ettinger scheme, for which purpose the mixing and aeration zones have been designed in the aeration tanks. The mixing zone is equipped with a submersible electromechanical mixer to prevent sedimentation of the sludge. Aeration system based on disk aerators produced by Ecopolymer PE (village of Polotnyany, Kaluga region) is provided in the aeration zone of the aeration tank. Internal recycling of wastewater in aeration tanks is carried out with the help of low-pressure inner circulation submersible pumps.
Air for wastewater aeration in aeration tanks is supplied by blowers. According to the project, the blowers are installed in the existing production building. The capacity of the blowers is controlled by the frequency converters (hereinafter referred to as "inverters").
Separation of wastewater and biological sludge is provided in vertical secondary sedimentation tanks.
Description of the sedimentation treatment process scheme. During the treatment of wastewater from Kaluzhskaya Poultry Farm JSC, the following types of sedimentation are formed:
Excess biological sludge is pumped out by pumps to disk thickeners located in the mechanical treatment and sludge dewatering building. The capacity of the excess biological sludge pump is controlled by an inverter. To improve the water-yielding properties of excess sludge, a flocculant solution is added to the excess sludge before its thickening. The dosing of the flocculant solution is carried out by dosing pumps installed in the mechanical treatment and sludge dewatering building.
The working solution of the flocculant is prepared using the units for the preparation of chemical solutions from a dry powder.
The thickened biological sludge is accumulated in the sedimentation tank, where the raw sludge and floating substances from the primary sedimentation tanks are also fed to. To prevent silting of the reservoir, an electromechanical submerged mixer is installed in it.
A sedimentation mixture is pumped by pumps out from the tank for further mechanical dehydration. The capacity of the excess biological sludge pumps is controlled by an inverter. Mechanical dehydration of sludge to a design humidity of 78% is carried out on belt filter presses. Sediment from the tank is fed into the flocculator of the filter press; to improve the water-yielding properties of the sludge, a flocculant solution is dosed there with dosing pumps.
The flocculated sediment is fed by gravity to the belt filter press. The dehydrated sediment is transported by trucks to the SHW landfill for dumping.
The filtrate and wash water from the disk thickeners and the belt filter press are fed by gravity into the filtrate tank. Dehydrated excess biological sludge is taken to the SHW landfill.
The designed automated process of wastewater biological treatment and the shop for mechanical sludge dewatering are of interest.
2.2.1. Automation of the wastewater biological treatment plant
This plant is equipped with Endress&Hauser nstrumentation.
The project provides for the installation of three operator stations (OP), which collect all the information necessary to monitor the process parameters and the state of process equipment related to a certain site. The location of the operator's station is provided in:
The operative control of process equipment is provided:
The amount of wastewater entering a block of biological treatment tanks is measured according to the readings of Promag 50W3H electromagnetic flowmeter. The flow meter readings are displayed on the operator's station No. 2.
The air flow supplied by the blowers is measured using Proline t-mass B 150 thermal mass flowmeter.
Process control of concentrations of suspended solids, or doses of biological sludge, and dissolved oxygen in the aeration tanks is performed on stationary Endress&Hauser devices:
Readings of the analytical instruments are displayed on the operator's station No. 2.
The plant is equipped with an automatic control of the degree of opening and closing of valves installed on air ducts, suitable for aeration systems of the aeration tanks.
The blower output is controlled by the pressure sensor installed on the main discharge air duct. Thus, automatic regulation of air supply to the aeration tanks is implemented in strict accordance with its required quantity for the passage of the technological process. The application of the biological control automation system made it possible to simplify the operation of the wastewater treatment plant. The local airflow control loop practically ensures energy savings of 25-32% during operation of the blowers in comparison with the constant uncontrolled mode of their operation.
2.2.2. Automation of mechanical sludge dewatering process
The mechanical dewatering of the raw sludge and compacted biological sludge formed in the wastewater treatment plant of Kaluzhskaya Poultry Farm JSC is implemented on EFP-L 1.0 modernized belt filter presses produced by Ecopolymer PE. One of these updated filter presses was shown at Equatec-2014 exhibition in Moscow .
All equipment of the mechanical dewatering shop is designed for periodic operation and for a specific amount of sludge. Enabling of all process equipment and its shutdown is carried out automatically in accordance with the signals of the level gauges in the silted reservoirs. Equipment of the mechanical dewatering shop processes the specified volume of sediment and switches off automatically. The dosing of the flocculant solution is provided in proportion to the flow rate of the incoming sludge and is specified during the commissioning. The flocculant solution preparation station operates fully automatically and does not require operator intervention, except for the cases of filling the hopper with the flocculant. The filter press is flushed automatically; pressure sensors are installed on the technical water supply lines to warn the operator if the pressure in the service water network is lower than 5 bar, displaying the corresponding message on the control cabinet. In the event of failure of sludge feed pumps, flocculant pumps, filter press, etc. the control system produces the "Alarm" signal and all the process equipment of the mechanical dehydration shop is automatically withdrawn from operation. After completing the processing of the sludge on the belt filter press, the washing pump continues flushing the belt filter press according to a predetermined algorithm, after which it is switched off too.
In 2015, MY PROJECT JSC completed design and delivery of process equipment for local wastewater treatment plant of the poultry factory Tambov Turkey LLC. Currently, construction and installation works of local wastewater treatment plant are in process.
In this project, the automation biological treatment system - a unit for separating the sludge mixture by submerged hollow fiber ultrafiltration membranes is of interest. According to the project, the operation of the membrane bioreactor (hereinafter - MBR) is fully automated, and will not further require constant presence of maintenance personnel to operate it.
The MBR automation will reduce the so-called "human factor" in its operation, i.e. eliminate possible errors of the maintenance personnel in operation of the MBR control system.
The application of the automation wastewater treatment system at the local wastewater treatment plant makes it possible to simplify the process of its operation and to reduce the amount of electricity consumed by the equipment. At present, an indispensable condition for the design of wastewater treatment plants is the development of an automated process control system. MY PROJECT implements customized automation schemes for wastewater treatment plants "on a turn-key basis" for both food enterprises [4-6] and municipal wastewater treatment plants .
Poultry farm wastewater treatment plant automation