Joint Application of the Fine-Bubble Aeration System and Vortex Airlift Device for Municipal Waste Water Biological Treatment

Size: px

Start display at page:

Download "Joint Application of the Fine-Bubble Aeration System and Vortex Airlift Device for Municipal Waste Water Biological Treatment"

Ashlie Mills
6 years ago
Views:

1 Joint Application of the Fine-Bubble Aeration System and Vortex Airlift Device for Municipal Waste Water Biological Treatment Andreev Sergey Yurievich Doctor of Technical Sciences, Professor, Department «Water Supply, Sewerage and Hydraulic Engineering» Grishin Boris Mikhailovich Doctor of Technical Sciences, Professor, Head of Department «Water Supply, Sewerage and Hydraulic Engineering» Garkina Irina Aleksandrovna Doctor of Technical Sciences, Professor, Department «Mathematics and mathematical modelling» Kamburg Vladimir Grigoryevich Doctor of Chemical Sciences, Professor, Department «IT systems» Penza State University of Architecture and Construction Demidochkin Vitaliya Vasilyevich Candidate of Technical Sciences, Assistant Professor, Head of Department «Heat and Gas Supply, Ventilation and Hydraulic Engineering» Orenburg State University, 13, Victory Av, Orenburg, Russia. Abstract The article represents data concerning investigational studies of water mixing process in the aerated tank using diffuser tubes and vortex airlift device (VALD). It has been established that application of VALD enables to increase performance of the aerating fine-bubble system by 1,6-1,7 times. Here are the laboratory study results of municipal waste water biological treatment by activated sludge under combined application of the fine-bubble aeration system and the VALD. The proposed combined method of aeration enables to reduce suspended substances, ammonium nitrogen concentration and oxidizability by 10-15% and phosphate concentration by 22% in treated water as compared with the fine-bubble aeration technology. Keywords: tap water, municipal waste water, aerating volume, aeration intensity, mass transfer volume factor, finebubble aeration system, vortex airlift device, combined aeration system, activated sludge, biological treatment, suspended substances, oxidizability, ammonium nitrogen, phosphates. INTRODUCTION Operating practice of modern waste water aerobic biological treatment facilities shows that 60-80% of treatment cost depends on the effectiveness of used aeration system being the most power-intensive element of a treatment plant [1]. The fine-bubble pneumatic aerating systems with air bubble diameter of 1-4 mm are the most common for the technologies of municipal and industrial waste water treatment in aerotanks [4]. Performance of the pneumatic aerating system can be radically increased by additional liquid mixing in the aerating volume. According to [5], oxygen mass transfer volume factor in liquid K La (h -1 ) representing efficiency of the aerating process is the function of the specific output required for mixing of the aerating volume unit N у (W/m 3 ) where А is an empirical factor. K La=A N y 0,95, (1) The method of additional mixing in the aeration basin is used in the combined pneumatic mechanical aerating system. The disadvantage of the pneumatic mechanical aerating systems is 11009

2 that each aerator needs a motor, a gearbox, and a balance system for rotating parts. This fact complicates significantly the aerator operating process, reduces its reliability and increases its cost. Vortex airlift devices are intended to be a substitute for machine mixers that enable escaping disadvantages typical for pneumatic mechanical aerating systems. The vortex airlift device (VALD) design has no rotating parts that significantly simplifies its operation [6]. A highly turbulent air-water flow is generated in the VALD shaft resulting in improvement of mass transfer characteristics in the liquid air bubble system. Study objectives in this work paper were: 1) to study the efficiency of combined operation of fine pneumatic aerating systems and VALD at aerating clean tap water volume; 2) to evaluate the efficiency of municipal wastewater biological treatment by activated sludge using the fine-bubble aeration system and VALD. MATERIALS AND METHODS Experimental studies of aeration and liquid mixing using vortex airlift were conducted at the laboratory installation (Fig.1) situated at the waste water treatment plant pumping station of Penza. Fig.1. Laboratory installation scheme: 1 tank, 2 VALD, 3 pipe aerators, 4, 4 / rotameters, 5 compressor, 6, 6 / valves The laboratory installation consisted of a tank 1 for 1.0 m 3 of water, two Aqualine fine-bubble aerators 3 of 32 mm in diameter and 0,5 m in length each, a vortex airlift device 2 with the shaft of 50 mm in diameter and 630 mm in height, a compressor supplying the air to the aerators and the VALD. Water depth in the tank 1 was 1,2 m. Compressed air flow supplied by the compressor 5 to the tube aerators and the vortex airlift device was monitored by rotameters 4, 4 / and was controlled using valves 6, 6 /. At the first stage of the study, the dependency of the volume factor of oxygen mass transfer to the tap water К La on the aeration intensity value J as well as on the ratio of airflow supplied to the VALD (Q в) and the aerators (Q а) was determined during simultaneous operation of Aqualine finebubble aerators and the VALD. The intensity range J varied from 5 to 20 m 3 /m 2 h. The value of the mass transfer volume factor К La being indicative of the relative oxygen amount transferred to the liquid volume unit per unit of time was determined in accordance with the reference method of variable oxygen deficit. When using this method, water deoxygenation was performed followed by increase in dissolved oxygen concentration during aeration process with the specified aeration intensity. Water oxygen concentration was measured with АТЕ012 dissolved-oxygen meter. The mass transfer volume factor was determined by the formula: K 1 C C s 1 La ln, (2) T2 T1 Cs C2 where С s is oxygen concentration in water at its complete saturation, mg/l; С 1 oxygen concentration in water, mg/l, at the beginning of the aeration process (time point Т 1, h); С 2 oxygen concentration in water, mg/l, at the end of aeration (time point Т 2, h). At the second stage of the study, the tank 1 (see Fig. 1) was filled with municipal waste water taken from the city 11010

3 treatment facilities, followed by activated sludge from the existing aeration tanks. Waste water composition was as follows: - suspended substances mg/l; - oxidizability mgо 2/l; - ammonium nitrogen (NH 4 ) ,5 mg/l; - phosphates (РО 4 ) - 9-9,2 mg/l. Activated sludge concentration in waste water was 3 g/l. The obtained mixture of waste water and activated sludge was aerated in the first experimental series using only the finebubble aeration system, and in the second experimental series using combined operating aerators and VALD with the optimum air flow ratio obtained according to the results of the first stage of the study. Aeration intensity in all series of the second stage of the study was within J=5,8-15,6 m 3 /m 2 h, aeration time was 4 hours. During the aeration process, the samples were regularly collected from the upper part of the tank 1 and then they were settled down for 2 hours in the 1 L laboratory glass test jars. The suspended substances in the treated water after settlement were determined using the weight method. The oxidizability was determined using the complete potassium dichromate oxidation method. NH 4 ions concentration in water after treatment was determined using Nessler's reagent, and colorimetric method was used to identify phosphate ions concentration. RESULTS AND DISCUSSIONS The results of the first stage of the experimental study of oxygen mass transfer into tap water at its aeration by Aqualine fine-bubble aerators and mixing by the vortex airlift device are presented in diagrams (Fig.2). Fig.2. Dependency of mass transfer volume factor К La on aeration intensity J and relative air flow supplied to the vortex airlift devic Qâ Q 1 Q =0; 2 Q =0,05; 3 Q =0,10; 4 Q =0,2 Q a Analysis of the diagrams shows that additional high turbulent mixing of the air-water flow and generation of recirculation mode in the tank due to VALD application allowed increasing the efficiency of combined aerating system within the aeration intensity range J=5-20 m 3 /m 2 h. Subject to power consumption, the most optimum condition for combined operation of the fine-bubble aeration system and VALD was observed with the air flow rate of Q 0, 10 (see Diagram 3, Fig. 2). Combined aeration system value К La increased by 1,6-1,7 times for the specified mixing mode in all range of mixing intensity J as compared with the fine-bubble aeration system operation. At the second stage of the study, the results of biological treatment of waste water using activated sludge after aeration with the fine-bubble aeration system (1 experimental series) were compared with the combined aeration system with VALD with regard to expense ratio for the fine-bubble aerators and the VALD (2 experimental series). The values of suspended substances and oxidization characteristics for the sewage waters are represented in Fig. 3, the values of NH 4 ion concentrations in water after settlement are shown in Fig

4 Fig. 3. Diagram of residual values of suspended substances and oxidization characteristics in sewage waters: 1 and 2 for finebubble aeration system at J 1=5,8 m 3 /m 2 h and J 2=15,6 m 3 /m 2 h; 3 and 4 for combined aeration system ( Q 0, 10 ) at J 1=5,8 m 3 /m 2 h and J 2=15,6 m 3 /m 2 h Fig. 4. Diagrams of residual values of ammonium nitrogen and phosphates in sewage waters: 1 and 2 for fine-bubble aeration system at J 1=5,8 m 3 /m 2 h and J 2=15,6 m 3 /m 2 h; 3 and 4 for combined aeration system ( Q 0, 10 ) at J 1=5,8 m 3 /m 2 h and J 2=15,6 m 3 /m 2 h The analysis of obtained results showed that the use of combined aeration system with VALD allowed reducing pollution load in all factors tested as compared with the finebubble aeration system at equal aeration intensity. At J 1=5,8 m 3 /m 2 h, the suspended substances concentrations in sewage waters reduced from 16,0 mg/l to 14,0 mg/l (Diagrams 1 and 2, Fig.3), at J 2=15,6 m 3 /m 2 h this factor reduced from 14,6 mg/l to 12,4 mg/l (Diagrams 3 and 4, Fig.3). At the same J 1 and J 2 values, the residual oxidation value in sewage waters 11012

5 reduced from 42,0 mgо 2/l to 37,2 mgо 2/l and from 36,0 mgо 2/l to 32,8 mgо 2/l, respectively (see Fig. 3). NH 4 concentrations at J 1=5,8 m 3 /m 2 h in treated sewage waters reduced from 9,0 mg/l to 7,7 mg/l and from 6,0 mg/l to 4,8 mg/l, respectively (Diagrams 1 and 2, Fig.4), at J 2=15,6 m 3 /m 2 h NH 4 concentrations changed from 5,2 mg/l to 4,4 mg/l and from 3,5 mg/l to 2,7 mg/l, respectively (Diagrams 3 and 4, Fig. 4). On average, due to application of the combined system with fine-bubble pipe aerators and VALD, the concentration of suspended substances in treated water reduced by 14%, oxidizability by 10%, NH 4 concentration - by 15% and phosphate concentration by 22% as compared with the application of fine-bubble aerators only. CONCLUSIONS 1) VALD used as a mixer together with the fine-bubble aeration system enables to improve its mass transfer capacity due to additional turbulization and recirculation of the water-air flow in the aeration volume. At the ratio of 1:10 for compressed air supply to the VALD and into the system of pipe aerators, the oxygen mass transfer volume factor for the aeration intensity range of 5-20 m 3 /m 2 h increases by 1,6-1,7 times as compared with the fine-bubble aeration system operation only. 2) In respect to municipal waste water biological treatment by activated sludge, the use of combined aeration system with VALD makes it possible to reduce the concentration of suspended substances by 14 %, oxidizability by 10%, ammonium nitrogen by 15 % and phosphate ions by 22 % in treated water as compared with the fine-bubble aeration method. REFERENCES [1] Hentse, М., Harremdes, P., Jansen, L.C., Arvin, A., Waste water treatment. Moscow. Pages 480. [2] Voronov, Yu.V., Water disposal and waste water treatment. Moscow, ASV Press. Pages 702. [3] Karelin, Ya.А., Zhukov, D.D., Zhurov, V.М., Repin, B.N., Industrial wastewater treatment in aerotanks. Moscow. Stroyizdat. Pages 220. [4] Rao, D.G., Senthilkumar, R., Byrne, J.A., Feroz, S., Wastewater Treatment: Advanced Processes and Technologies. IWA Publishing and CRC Press. Pages 365. [5] Finn, R.K Agitation-aeration in the laboratory and in industry. Bacteriological views, 18: [6] Andreev, S.Yu., Grishin, B.М., Device for liquid aeration. Patent RU No

Compact Waste Water Treatment MBR /MBBR Technology

Compact Waste Water Treatment MBR /MBBR Technology 1 Minimal Operation and Maintenance Costs and use of Chemicals 2 Recycle and Reuse water for Irrigation and Recreation 3 Save Water, Energy, Money and