Commissioning - the key stage of putting wastewater treatment plants into operation

M.A. ESIN ¹ , A.V. SMIRNOV ² , A.N. SOKOLOV ³

¹ Esin Mikhail Anatolievich, PhD in Engineering, Head of Process Department, MY PROJECT JSC, floor 8, bld. 7, B. Strochenovsky Lane, Moscow, Russia, 115054, tel.: (495) 981-98-80, доб. 273, e-mail: yesin@myproject.msk.ru

² Smirnov Aleksandr Vladimirovich, Leading Engineer of Process Department, MY PROJECT JSC, floor 8, bld. 7, B. Strochenovsky Lane, Moscow, Russia, 115054, tel.: (495) 981-98-80, ext. 277, e-mail: smirnovav@myproject.msk.ru

³ Sokolov Aleksei Nikolaevich, Engineer of Process Department, MY PROJECT JSC, floor 8, bld. 7, B. Strochenovsky Lane, Moscow, Russia, 115054, tel.: (495) 981-98-80, ext. 275, e-mail: sokolov@myproject.msk.ru

This paper deals with the issues related to the commissioning of the equipment and wastewater treatment plants. A brief review of the history of commissioning the facilities in the Soviet Union and in modern Russia is given. The problem areas of adjusting every equipment assembly, the algorithm of work performance and the required results are shown. The achievement of sustainable performance is provided by quality and skilled commissioning. Correct visual evaluation of the equipment state carried out during the acceptance for commissioning procedure is very important. Non-detected defects and faults in the process line will cause fast assembly fail which can result in an accident. The principles of My Project activities related to commissioning are presented. Special attention is paid to adjusting biological treatment in aeration tanks: from the front end engineering to the routine maintenance of the assembly.

Key words: plant reconstruction, commissioning, installation supervision, wastewater, mechanical treatment, biological treatment, post-treatment.

Qualified commissioning at wastewater treatment plants is a key to their subsequent successful operation and achievement of the standard quality of treated wastewater. The purpose of commissioning works is to adjust process equipment and constructed/reconstructed plants and ensure their design parameters. Adjustment begins with the analysis of design solutions, inspection and acceptance of construction and installation works. During the commissioning process, shortcomings and inconsistencies in design solutions are identified that can adversely affect the safety and efficiency of operation of the facilities. If necessary, a set of corrective measures and technical solutions for the successful commissioning of wastewater treatment plants is developed.

In the USSR, the republican trust "Rosvodokanalnaladka", which carried out a wide range of engineering works such as commissioning of engineering networks, systems, structures, communications, etc., was engaged in commissioning in the sphere of water supply and sewerage. The work was based on contractual relations between the trust and the Ministry of Housing of the RSFSR. All the production departments of the municipal water supply and sewerage (PDWSS) transferred funds for the development of the industry to the ministry and separately applied for work in the region. On the basis of the reviewed and approved application, a contract and estimates were drawn up. The final stage was the report, which was set forth by a completion certificate.

In the 1990s, the well-established relations and interaction of communal enterprises were destroyed, Rosvodokanalnaladka trust almost completely lost its positions. The development of market relations has contributed to the rapid replacement of a previously monopolistic organization by foreign companies offering advanced technical solutions and a wider range of services. Domestic enterprises, practically from scratch, mastered new equipment, technologies, concepts of system management and provision of competitive services to WSS enterprises. Since then, specialized organizations ceased to exist, performing the functions of pre-commissioning and commissioning. Commissioning was limited at best to the configuration of individual units or equipment offered by individual companies.

Proper self-commissioning requires a thorough study of the regulations (in some cases, an adjustment or development of a new document is necessary) and knowledge of industry regulations. As experience shows, commissioning is not given enough attention, especially when developing design estimates. At the same time, the presence of complex modern engineering solutions and technologies complicates the already difficult task of putting equipment and facilities into operation. Only companies with a staff with practical experience and sufficiently high level of qualification are authorized to carry out commissioning of modern facilities.

During the commissioning process, possible violations during installation, defects in equipment prior to the start of its operation, and its uninterrupted operation throughout the entire operation period are detected. In fact, the task of commissioning is the final inspection and practical adjustment of the process mode of operation of structures for their trouble-free subsequent operation.

My Project has a separate subdivision engaged in commissioning and subsequent servicing. At the same time, process engineers are engaged in technological adjustment, participating in the development of the basic project and accompanying its implementation from design to commissioning. In setting up wastewater treatment plants, the company's specialists are guided by the following basic rules:

• the preparatory stage of commissioning is a visual inspection, analysis of work performed for compliance with design solutions, quality control of installation and erection of equipment, readiness of facilities and equipment for commissioning;
• close cooperation with the wastewater treatment laboratory in developing a laboratory control plan for the commissioning period, additional sampling and laboratory observations (chemical analysis of wastewater, laboratory tests, etc.);
• interaction with the process engineers of wastewater treatment plants: discussion of the plan and stages of process adjustment, optimal operating modes (including emergency response measures), the main methods of quality control; approval of the interaction scheme for the period of commissioning and the development of a new work schedule for all facilities or a separate process unit;
• presence of company representatives at the facility until the stable indicators of treated water are achieved with observance of the standards (SNiP 3.01.04-87 "Acceptance of Completed Facilities for Construction"). Signing of the completion certificates after the integrated testing of facilities within 72 hours;
• operational and engineering staff training;
• preparation of the technical report after the completion of the commissioning in accordance with the regulatory industry documents.

My Project  for its 25 years of activity in design and start-up of wastewater treatment plants has acquired extensive experience in commissioning. Adjustment of each unit has its technical aspects, meeting which will allow the setup and accepting organizations to focus on the early achievement of the result. The authors tried to generalize the accumulated experience and summarize it in this paper.

A variety of equipment at wastewater treatment plants makes it difficult to choose for reconstruction or construction of new ones. For example, the most common mistake is the replacement of a screen similar in design parameters. The result of this replacement is a return to the same problems of treatment quality and screen operation. The engineering task of choosing screens is primarily to develop several options for installing screens of different types, subject to the specific composition of the wastewater and the plan for the future development of structures as a whole. The evaluation of the screen operation is characterized by the effectiveness of waste trapping and its humidity. Table 1 presents the comparative characteristics for determining the parameters of the effective operation of the screens [1].

 

Screen type	Bar spacing size, mm	Main process applicability	Waste trapping efficiency	Screened waste humidity*, %
Rack	5-40	Coarse and moderate filtering	Low	85-95
Curved	2.5-50			85-95
Band	1-10	Moderate and fine filtering		85-95
Drum	0.2-6	Fine filtering	High	40-75
Screw	0.5-6			40-75
Step	1-6		Moderate	60-85
* Without waste thickener.

Coarse and moderate filtering

Low

Low

Fine filtering

High

Fine filtering

 

The modern level of automation allows minimizing the proportion of manual operations, the presence of operators and the number of emergency situations. In-plant screens are equipped with a sufficient amount of automation and control facilities, which simplifies their launch and reduces the subsequent operation only to scheduled inspections.

Modern wastewater treatment plant can use either factory-made grit removals (low-capacity plant) and classic concrete ones. Effective grit removals protect pumps, mechanisms, sludge dewatering equipment (especially centrifuges) from sand abrasion. Non-removed sand accumulates in the raw sediment of primary sedimentation tanks, increases its ash content, which makes it difficult to discharge raw sludge and leads to increased energy costs when transporting it through pipelines, complicates the subsequent treatment of the sediment (for example, during fermentation).

During the setup and commissioning of the grit removal (regardless of its type), attention should be paid to the following characteristics: the sand content in the sediment (ash content); water flow rate; wastewater retention time; the efficiency of removing the sand of a given fraction; humidity of the sand pulp.

Observance of the optimum speed regime will allow for effective operation of the grit removals without violation of the subsequent industrial processes, and the use of hardware solutions for sand dewatering significantly reduces transportation and disposal costs. Table 2 shows the optimal parameters of the effective work of the grit removals [2].

 

Type of grit removal	Sand content in sludge, %	Water flow rate, m/s	Retention time, s	0.2 mm sand removal efficiency, %	Sand pulp humidity, %
Tangential	70-75	0.6-0.8	30-50	80-85	Up to 20%
Horizontal	55-60	0.15-0.3	120-600	90-95	96-98
Aerated	90-95	0.8-2	180-900	> 95	96-98

 

The main process factor ensuring uninterrupted operation of sedimentation tanks is observance of the following specified parameters: humidity, ash content, density of raw sediment; sand content in the wet cake; distribution of flow rates in the sedimentation field of suspended particles.

Acceptance of primary sedimentation tanks implies checking the level of the overflow edge of the catchment trays troughs for clarified water and the mouth of the inlet, the quality of the concrete work and the smoothness of the bottom of the sedimentation tank. Construction errors may impair the operation of the sedimentation tank, and after commissioning, will not be subject to correction.

The distribution of wastewater between sedimentation tanks in the group, that is, the operation of the distribution chamber is of great importance. Service personnel should check the individual flow rates daily, in the hours preceding the maximum inflow of wastewater, avoiding their excess. Particularly important is the control of the operation of the distribution chambers during the periods of stopping individual sedimentation tanks for repairs, since with a smaller number of operating facilities, the load fluctuations at each sedimentation tank are more obvious, primarily at small and medium-sized wastewater treatment plants.

An important condition for the stable operation of the primary sedimentation tank is the timely removal of the settled and floating substances from it.

The operation of the primary sedimentation tanks requires monitoring the humidity of the sediment and its level of stand. Usually the sediment is removed 1-3 times a day. The actual frequency is determined experimentally and depends on a number of factors: the concentration of suspended solids in the incoming water, the hydraulic load on the sedimentation tank, the presence of the acidification process, etc.

For biological treatment of effluents, the wastewater treatment plants use biological sludge or biofilm (aeration tanks or biofilters, respectively). The most widespread are aeration tanks of various configurations and sizes with biological sludge.

During the adjustment of aeration tanks, special attention should be paid to their process and technical parameters. Process parameters: characteristic of biological sludge (volumetric weight, mass dose, sludge index, load on organic and biogenic substances, age); characteristics of aeration tanks (process scheme, volume and time of retention in each zone); amount of circulating sludge (internal and external recycles). Technical parameters: characteristics of the equipment used (aeration system, mixers, pumping equipment); characteristics of wastewater (flow, concentration); characteristics of the facilities (sedimentation tanks, aeration tanks).

Also, before starting setup of treatment plants, it is necessary to approve the program of its implementation, create a log and organize the work of the operational staff, chief process engineer and laboratory. It should be noted that the setup log is the most important document, as it forms the basis of the future report, the regulations for the operation of facilities, and also a kind of timing of the work, which allows analyzing errors, sharing experiences with colleagues, etc.

Before the startup, the design documentation is checked for compliance with the actual state of the aeration tanks: equipment, process flow diagram, the quality and quantity of incoming wastewater, the amount of air supplied and the volume of circulation. If the project does not meet the requirements, the changed parameters should be entered in the setup log.

The adjustment of the aeration tanks should start from the initial setting of the oxygen regime in the zones of aeration and the implementation of effective nitrification, establishing the design distribution of the supply of wastewater and return sludge. These activities form the basic state of adjustment. Particular attention at this stage should be given to the initial biological sludge - its characteristics and the experience of operation under the old scheme (problems, treatment efficiency, microbiological characteristics) must be studied. When working with activated sludge, it should be borne in mind that biocenosis of biological treatment is very inert, and the initial performance of sludge will be similar to the existing state of affairs. A complete transformation of the biological sludge occurs over a period equal to at least three of its ages, i.e. if the age of sludge is 12 days, then it will completely renew no later than after 36 days. The required indicators will be achieved after the renewal of the sludge biocenosis.

During the entire time of formation of a new biocenosis of biological sludge, it is necessary to constantly monitor and correct the oxygen regime both in the aeration and in the mixing zones. After a half of the adjustment work (1.5-2 of sludge age), the quality of denitrification is evaluated (in the case of nitri-denitrification schemes). In case of low efficiency of nitrate removal, the wastewater supply to the mixing zones is adjusted, as well as the volumes of biological sludge circulation (internal and external recycles). When the required quality of denitrification is reached, the process of biological phosphorus removal should be adjusted.

The domestic literature uses for the process of biological removal of phosphorus the term “dephosphatization”, which is an inaccuracy, since in the mixing zone there is an increase in phosphorus concentration - phosphatization, and in the aeration zone its concentration decreases - dephosphatization. Therefore, the world practice uses the adopted term "deep biological phosphorus removal", which implies the sum of phosphatizing and dephosphatizing processes (in foreign sources the process is called enhanced biological phosphorus removal (EBPR) [3].

Setting up the process of enhanced biological phosphorus removal is a complex technological task, but as experience shows, it is possible to achieve stable and complete purification from phosphorus. Even in the unconfigured “aeration tank - secondary sedimentation tank" system, phosphorus removal sometimes proceeds efficiently. Allocation of mixing zones (anaerobic zones) and the organization of internal recirculation of the biological sludge enhances phosphate removal efficiency due to the growth of phosphate-accumulating bacteria - enhanced phosphorus removal takes place. The efficiency of phosphorus removal by biological means is greatly influenced by the regulations for the removal of excess sludge [4].

The adjustment of the process of enhanced biological phosphorus removal consists in the distribution of the organics of the incoming wastewater between the denitrification in the anoxic zones and phosphatization in the anaerobic zones. The conventional process schemes (AO, VIP, UCT, MUCT, etc.) [5] imply anaerobic zones without medium and high concentrations of nitrates, and completely exclude the presence of dissolved oxygen. As practice shows, the organization of an anaerobic zone in a separate reservoir always ensures a more effective purification from phosphorus. It should also be borne in mind that when the phosphorus is completely removed by biological means, the sludge volume increases, which in turn should be taken into account in the regulations for the operation of sludge pump stations, the calculation of sludge age and the amount of excess sludge.

The adjustment of the process of biological treatment is a key link in the operation of the entire plant system. This unit plays a crucial role in ensuring the standard quality of treated water. To increase the efficiency of the adjustment process, the specialists of My Project necessarily apply mathematical modeling of biological treatment processes. Modeling allows determining the optimal process modes of operation of the plants with varying loads and other factors.

The modeling computer program conventionally divides the aeration tank into ideal mixing reactors equipped with independent adjustable air, wastewater, return and circulation sludge ducts. The results of mathematical modeling make it possible to determine the basic process parameters of the operation of the “aeration tank - secondary sedimentation tank” system: oxygen concentration, flow rates (wastewater, return sludge, sludge mixture of internal recycle), and the treatment quality at each site (Fig. 1).

Fig. 1. Example of the interface of EcoSim mathematical modeling program

Proceeding with the setup, the oxygen regime profiles and the treatment efficiency modeled for each conventional reactor describing a separate section of the aeration tank (pollutant profile) are used. Thus, ensuring the compliance of the calculated and actual values ​​of the aeration tank, the required quality of treatment is achieved. Modeling helps to check a huge number of variants of process schemes, modes of operation of facilities (standard, emergency, flood, etc.), and wastewater concentrations.

After completion of the setup of the aeration tanks, the process maps for the operation of the biological treatment unit are formed, which are basic for drawing up the operating procedure for the plant. Process maps are developed for two scenarios of aeration tank operation: a standard mode map and an emergency map. Emergency operation maps include regimes when pollutant concentrations, equipment operation, wastewater and/or biological sludge flow rate do not correspond to design parameters.

Such maps can be drawn up both for temporary operation, with a short-term violation of the established operating efficiency, and with a constant (increase in the concentration of substances, flow rates, etc.), but subject to the quality of treatment. In case the facilities are continuously operated using an emergency process map, the design solutions should be revised.

The final stage of setup involves training of the wastewater treatment plant staff of all levels of management. In particular, the operational staff is additionally trained during the operating period, as it is its direct participant.

The main purpose of wastewater post-treatment plants is to meet the requirements for discharge into water bodies in terms of suspended substances, organic compounds and phosphorus (for chemical dephosphatization).

The flow rate of wastewater supplied to the post-treatment filters, in contrast to the high-rate water pretreatment filters, has a high degree of unevenness, especially in industrial wastewater [6]. Compliance with the uniform distribution of wastewater entering each post-treatment filter, as well as the routine filtration rate, must be given special attention in order to ensure the design filtering parameters and, accordingly, the high treatment efficiency. The number of operating filters is selected based on the flow rate of water entering the post-treatment. Before setup, it is necessary to calculate the inflow graphs for a particular object similarly to those shown in Fig. 2.

Fig. 2. Relation of the number of operating filters to the wastewater flow rate

 

inflow non-uniformity coefficient: 1 – 2 (unit capacity q₁ = 290 m³ /h); 2 – 1.5 (q₁ = = 375 m³ /h); 3 – 1.1 (q₁ = 510 m³ /h)

The greater the unevenness of the water supply for its post-treatment, the less time the filters will operate and the higher the actual filtering rate is. The incoming water should be distributed as evenly as possible between the operating high-rate filters. In this sense, there are no disadvantages of drum and mesh disk filters, they have compact design and are less energy-intensive in operation, but the efficiency of their operation is much lower than that of granular media filters.

Modern solutions for wastewater post-treatment must be implemented with a high degree of automation, since the achievement of efficient operation of filters manually requires a deep knowledge of filtration processes from engineering personnel and operational staff. The introduction of automated control systems for the operation of a group of filters makes it possible to perform the basic process of clarifying and washing the filtering material (media, disk, mesh) with constant monitoring of the main parameters.

Much attention has been recently given to the problems of sediment dehydration. As an alternative to natural methods of dehydration, which require large areas of land, centrifugation, filter pressing on chamber and belt presses are widely used. The simplest in the design is the dewatering method for belt filter presses, but the choice of the dewatering method is an individual task, the solution of which depends on the performance of the plant and the nature of the treated sludge. Comparison of sludge dewatering methods (Table 3) shows that each of them has both certain advantages and disadvantages [7; 8].

When selecting the dehydration devices, the peculiarities of the sediment and local operating conditions must be taken into account. The sludge dewatering technology place a high importance on rational use of reagents. Determination of the optimal dose of reagents is a very complex and responsible task, since in practice there is a simultaneous change in a number of factors. Prior to setup, the company's specialists conduct preliminary pilot-industrial tests to determine the moisture release properties of the sediment, to select the type of flocculant and its optimum dose for the process.

 

Press type	Sludge humidity, %	Occupied area	Power consumption, kW*h/t dry matter	Operation mode	Filter quality	Flush water flow rate
Belt	70-80	High	10-25	Continuous	Clean	High
Chamber	60-70	Moderate	20-40	periodic	Low quality	Low
Centrifuge	65-75	Compact	30-60	Continuous	Clean	Low

 

We should note the importance of static observations and comparisons of the main process parameters. A comprehensive analysis of complex technological situations that arise during the operation of treatment facilities requires considering all possible solutions to problems subject to the material balance of hydraulic loads and pollution, and choosing the optimal mode. System analysis provides for information, which makes it possible to make fundamentally new solutions for early achievement of setup indicators.

All process regimes are recorded in the "Design (Standard) and Real Performance Indicators Log". In practice, the analysis of logged materials greatly simplifies the adjustment work and allows accurately determining the causes of process violations when the object achieves the design parameters.

This paper presents general trends and rules for setup. Experts of Ecopolymer have launched more than 50 natural and wastewater treatment plants. A number of objects has faced certain difficulties; it was not always possible to immediately achieve the desired result. However, our experience and qualifications allowed us, in the final analysis, to achieve the required results at almost all plants. Today we perform integrated setup of wastewater treatment plants not only for our projects, but also for projects of other companies, having previously analyzed the process feasibility and efficiency of design solutions.

The achievement of sustainable performance is provided by quality and skilled commissioning. Correct visual evaluation of the equipment state carried out during the acceptance for commissioning procedure is very important. Non-detected defects and faults in the process line will cause fast assembly fail which can result in an accident.

Summary

Twenty-five years of fruitful operation of Ecopolymer in the Russian market have allowed it to take its rightful place among the organizations providing a full cycle of engineering services in the modern management of WSS projects. To date, the main activity of the company is the implementation of integrated construction and reconstruction projects for water supply and wastewater treatment plants - from the development of design estimates to the commissioning of facilities. Concerted efforts and the close-knit teams of all subdivisions of the company allows finding the optimal solution of any problem in the shortest possible time and launching equipment of any complexity. The main elements of the corporate values ​​of the company are the level of skills, personal responsibility and commitment to the interests of the customer. In general, they put before each employee the task of achieving the final result and providing technical and consulting support to the customer after completion of commissioning at the facility, for example, in case of emergency situations. Practical application of modern process solutions and equipment, along with innovations, as well as the accumulated experience ensure implementation of all the design ideas with maximum effect for the customer.

REFERENCES

1. Esin M.A., Sleptsov V.G., Sokolov A.N. Rekonstruktsiia reshetok: osobennosti i inzhenernye resheniia (Screen reconstruction: features and engineering solutions) // Voda Magazine. 2012. No. 12. p. 38–42.
2. Meshengisser Iu.M. Retekhnologizatsiia sooruzhenii ochistki stochnykh vod (Reengineering of wastewater treatment plants). – M.: «Izdatelskii dom «Vokrug tsveta» LLC, 2012. p. 211.
3. Smirnov A.V., Esin M.A. Puti resheniia neprostoi zadachi. Realizatsiia skhem biologicheskogo udaleniia fosfora iz stochnykh vod (Ways to solve a difficult problem. Implementation of schemes of biological phosphorus removal from wastewater) // Voda Magazine. 2014. No. 8. p. 4–9.
4. Rodionov A.N., Ozerova L.P. Retekhnologizatsiia aerotenkov dlia dostizheniia glubokogo udaleniia biogennykh elementov: opyt ochistnykh sooruzhenii g. Naberezhnye Chelny (Reengineering of the aeration tanks to achieve a deep removal of nutrient elements: the experience of wastewater treatment plants in Naberezhnye Chelny) // NDT. 2015. No. 2. p. 26–33.
5. Van Haandel A. C., van der Lubbe J. G. M. Handbook of biological wastewater treatment: design and optimization of activated sludge systems. – Elsevier, 2012. P. 770.
6. Ulchenko V.M. Doochistka stochnykh vod na filtrakh s zernistoi zagruzkoi (Wastewater treatment through the granular media filters) // Vodosnabzhenie i sanitarnaia tekhnika. 2010. No. 12. p. 34–38.
7. Meshengisser Iu.M., Kolesnik Iu.V., Esin M.A. Sovremennye metody i oborudovanie dlia obezvozhivaniia osadkov stochnykh vod (Modern methods and equipment for dehydration of wastewater sludge) // Vodoochistka. Vodopodgotovka. Vodosnabzhenie. 2011. No. 12. p. 24–34.
8. Liuft Ia.E., Oiiala T., Ruokanen L., Zinchuk O. Obrabotka osadka stochnykh vod: poleznyi opyt i prakticheskie sovety: Doklad komissii po okruzhaiushchei srede Soiuza Baltiiskikh gorodov (v ramkakh proekta po gorodskomu sokrashcheniu evtrofikatsii) (Wastewater sludge treatment: useful experience and practical advice: Report of the Commission on Environment Union of the Baltic Cities (under the urban eutrophication reduction project). – Turku, Finland, 2012. p. 125.

 

Commissioning