Full-scale application of microbial agent on in-situ sludge reduction

Xie Huifang1 Zhang Jinhua1 Xin Wenli1 Hu Canyang1 Yan Mei1Zhang Qing1 He Qihuan1 Zhou Jiancheng2

(1School of Environmental and Biological Engineering, Nanjing University of Science and Technology, Nanjing 210094, China)(2School of Chemistry and Chemical Engineering, Southeast University, Nanjing 211189, China)

Abstract：The full-scale application of Tx-1, a multifunctional microbial agent, was carried out for 8 months in an anoxic/oxic (A/O) municipal wastewater treatment process. The results show that the Tx-1 dosed system can obtain good effluent characteristics while minimizing sludge production and energy consumption. The total phosphorus (TP) is lower than 0.5 mg/L in effluent without any chemical regent added. The discharged dry sludge per 10 000 m3 wastewater Dwat decreases from 1.4 to 0.5 t. For per cubic meter wastewater, the air supply decreases from 6.0 to 5.1 m3 and the electricity consumption decreases from 0.412 - 0.425 kW·h to 0.331 kW·h. The addition of Tx-1 can improve the substrate removal constant and decrease the microorganism growth yield coefficient of activated sludge. At the same time, the structure of the microbial community changes and the biodiversity increases by adding Tx-1. The abundance of polyphosphate accumulating organisms (PAO), Comamonadaceae and Tetrasphaera, increased. Effective microbial agent is a potential way to combine in-situ sludge minimization with contaminants removal.

Key words：wastewater treatment; dosed anoxic/oxic (A/O) process; diversity of microbial community; kinetic parameters

Activated sludge process is widely used for biological treatment around the world, however, it also generates a large amount of excess sludge. In fact, treatment and disposal of excess sludge from wastewater treatment plants (WWTPs) has been a great challenge[1]. Current legal constrains, rising costs and public sensitivity to sludge disposal necessitate new development strategies for the reduction of excess sludge production[1-4]. Among various processes of minimizing the production of sludge, the in-situ sludge reduction technology appears to be an ideal one by reducing sludge production in the biological wastewater treatment process instead of post-treating the waste sludge[1,5].

It has been reported that microbial agents have wide applications in the fields of deodorization, bioremediation and the enhancement of biological treatment of wastewater[6-9]. There are some commercial products such as effective microorganisms (EM), Novozymes products and bio-form BTZ® products. However, compared with the application and research of microbial agents on improving the effluent, only few reports on reducing sludge production were carried out, especially for full-scale application[7-9]. Lack of full-scale application data and mechanism research has hindered their application and improvement[10-11]. Several pilot test cases reported in China showed that sludge reduction can be achieved by introducing microbial agents into the wastewater treatment line. Li et al.[12] screened two kinds of microbial agents and achieved 53.1% sludge in-situ reduction in an A2/O reactor (4.2 m3). However, a concomitant decrease in biological phosphorus removal occurred[11-12].

In the present study, a full-scale study on application of Tx-1, a kind of multifunctional microbial agent, is carried out in a WWTP with an average capacity of 23 408 m3/d. By introducing Tx-1 in the anoxic/oxic (A/O) activated sludge system and optimizing the operational conditions, the innovative system (Tx-1 dosed system) guarantees good effluent characteristics, particularly in the biological removal of total phosphorus (TP). At the same time, in-situ sludge reduction is achieved. The kinetic-parameters of the Tx-1 dosed system and the structure of a new microbial community are measured in the laboratory. The results prove that Tx-1 is an effective microbial agent for reducing sludge in-situ and enhancing phosphorous removal.

1 Materials and Methods

Tx-1 is produced by Shanghai Eco-Well Bioscience Co., Ltd in a pilot-scale fermentation system. The product is a light-yellow powder and consists of several kinds of facultative and aerobic stains. At the same time, the product also contains some enzymes and small molecules, such as organic acid, secreted in the fermentation process. Tx-1 has passed the safety-assessment on the application in environmental protection and obtained a security acceptance letter in Shanghai, China. Tx-1 is activated on site before using. Briefly, 20 g Tx-1 is added into 1 L influent, and the mixture is kept stirring in an activating tank at 30 ℃ for 12 h.

1.2 Full-scale pilot experiment

There are two A/O biological treatment lines (marked 1# and 2#) in the pilot plant. Swirling flow and micro-porous aeration equipment are equipped in two oxic zones, respectively, and the supplied air is adjusted by controlling the amount of aeration equipment. The water indices of effluent comply with the Grade Ⅱ standards in the national discharge standard of pollutants for the municipal wastewater treatment plant (GB 18918—2002, China).

Activated Tx-1 solution is added into the inflow of oxic zones continuously. The dissolved oxygen (DO) is controlled at 0.9 to 2.2 mg/L.

1.3 Analysis and data collection

During data collection, both the on-line and off-line monitoring indices are used. The on-line data of influent and effluent are recorded every day. Off-line indices of water (CODCr, BOD5, SS, NH3-N, TN and TP) and sludge (MLSS, SV30 and MLVSS) are measured every week in the plant laboratory.

The data are collected for one month (Stage 2) before the application of Tx-1 as the background data. After the start-up period of Tx-1 addition (15 d), the data is collected for eight months (Stage 3). The data from the same months (Stage 1) in the previous year is analyzed as the historical data. The influent water volume at different stages is shown in Tab.1.

1.4 Kinetic parameters

The kinetic parameters are determined based on the Lawrence-McCarty model and the Monod model[13-14] in our laboratory. The activated sludge is collected in the pilot plant and cultivated in two identical bioreactors (signed as Tx-1 dosed and Blank) under the following conditions: Temperature is 20 ℃; DO is 2 mg/L; and MLSS is 1.5 to 3.5 g/L.

1.5 Structure of microbial community

The structure of microbial community is analyzed by extraction, propagation and sequencing of DNA.

2 Results and Discussion

2.1 Effluent characteristics

The most important task for the pilot WWTP is to ensure the effluent quality, so the influent and effluent indices are monitored through the experiment and they are listed in Tab.2.

Compared to the historical and background values, the application of Tx-1 results in a significant increase of TP removal efficiency. Without adding any chemical phosphorus removal agent after biological treatment, the average TP content in effluent is less than 0.5 mg/L, the standard value of Grade IA in GB 18918—2002, China.

In terms of organic pollutants CODCr and BOD5, the removal efficiencies are similar to those in historical and background stages, and all the values are better than the drainage standard. It should be noted that similar removal efficiency is obtained with less air supply than the original process, which implies that the lower energy cost is available in the Tx-1 dosed system.

For nitrogen nutrients, it is found that the removal efficiency of TN and NH3-N is clearly affected by temperature. In July and August, the average water temperature is 27.2 ℃, and the average NH3-N and TN content in effluent are 6.4 and 17.4 mg/L, respectively, which can comply with the standard values of Grade I B in GB 18918—2002. However, when the average temperature decreases to 12.9 ℃ in February and March, the average NH3-N and TN content in effluent is 20.3 and 28.6 mg/L, respectively, which can only comply with the standard value of Grade Ⅱ. The nitrogen removal in A/O process is not so ideal in practical operation[15], so it is necessary to update the process in this plant in order to improve nitrogen removal. For microbial agents, adding some specially-selected strains with high nitrogen removal capacity at low temperatures should be considered.

2.2 In-situ sludge reduction

The MLSS in the oxic zone is set to be 2.0±0.5 g/L and DO 1.5±0.5 mg/L for the experimental stage according to prior studies. The characteristics of activated sludge and sludge production at different stages are listed in Tab.3.

Tab.3 Characteristics of activated sludge in an oxic zone and sludge production at different stages

After the addition of Tx-1, the ratio F of MLVSS to MLSS increases from 0.57 to 0.65, which indicates that the microorganism fraction has increased. Thus, the degradation activity of activated sludge increases, which perhaps is one of the reasons for the good performance in the dosed Tx-1 system at the lower DO concentration.

SVI results indicate that the sludge in the dosed Tx-1 system shows much better settle-ability than that in the original process. One of the major operational problems in the pilot plant is due to the poor settle-ability of activated sludge before the application of Tx-1. When MLSS is higher than 1.8 g/L, the flotation of sludge in the secondary clarifier often occurs. However, no more flotation of sludge occurs by adding Tx-1, even though MLSS is higher than 2.0 g/L. Good settle-ability can also provide a high concentration of return sludge. The relationship of sludge age and the ratio of XR/X in a steady state is[14]

where θc is the sludge retention time (SRT) or the sludge age, d; Q is the flow rate, m3/d; V is the volume, m3; R is the recycling ratio; X is the solid concentration in the aeration zone, mg/L; XR is the solid concentration in the return line, mg/L, and it can be roughly estimated as

So, it is clear that θc increases correspondingly when SVI and X decrease in the Tx-1 dosed system. Then the excess sludge (ΔX, g/d) decreases according to the following equation:

The statistical results in Tab.3 show that the discharged dry sludge per 104 m3 wastewater Dwat in the Tx-1 dosed system decreases by 64.3% and 45.5%, respectively, compared to the historical and background data. The sludge production per gram CODCr DCODwas only 48.8% of that at stages 1 and 2. The results show that effective in-situ sludge reduction is achieved in the Tx-1 dosed system.

Wastewater treatment is an energy-intensive process. In typical biological WWTPs, the aeration process accounts for more than 50% of the energy consumption[16-17] in order to supply DO for the microorganisms in sludge. So energy consumption can be significantly reduced when the oxygen requirement is reduced in the aeration process.

The aeration system in the pilot plant was designed to maintain DO at 2.0 mg/L, which is the average value in the activated sludge system[17]. However, the Tx-1 dosed system can be operated under a much lower DO concentration, which can be proved by the performance of line 2# in August at stages 1 and 3, respectively (see Fig.1).

The highest temperature appears in August in the pilot plant. The water temperature is 20 to 28 ℃ (Avg. 22.9 ℃) in Stage 1 and 26 to 30 ℃ (Avg. 28.1 ℃) in Stage 3, respectively, as shown in Fig.1. High temperatures lead to higher oxygen consumption due to the rapid biological reactions and the rapid oxygen depletion in the sludge[16], which means that more air supply is needed. Before Tx-1 application, another air supply fan (55 kW) was used to complement the DO during the high-temperature period from July to September in the pilot plant. However, it is not necessary at stage 3. So, at least approximately 1.0×105 kW·h electricity was saved in the summer.

Statistic results show that the DO content was low at stage 3. Even under the low DO concentration, similar removal efficiency of CODCr and NH3-N and the dramatic increase of TP removal efficiency were achieved. As shown in Tab.4, with the decrease of DO concentration, the average air supply per cubic meter wastewater decreases from 6.0 to 5.1 m3 in the oxic zone. Correspondingly, the aeration power requirements decrease. Also, the total electricity consumption per cubic wastewater decreases by 19.7% to 22.1%.

In this pilot plant, air supply was only adjusted by controlling the number of aeration equipment, so it was difficult to adjust the air supply volume according to the actual DO and designed parameters. Frequency conversion technology is strongly recommended to recast the operational model for the improvement of DO adjustment in the future.

2.4 Kinetic parameters

Two identical bioreactors were set up in our laboratory to compare the kinetic parameters of activated sludge with (Tx-1 dosed) and without (Blank) addition of Tx-1.

Tab.4 Statistical results of DO, air supply and electricity consumption at different stages

The following equations are used to calculate the kinetic parameters[13-14]:

where Y is the microorganism growth yield coefficient, mg/mg; v is the specific substrate utilization rate, 1/d; S0 and Se are the substrate concentration in the influent and effluent, respectively, mg/L; Xv is the biomass concentration, g/L; t is the hydraulic retention time, d; Kd is the microorganism decay coefficient,1/d.

where vmax is the maximum specific substrate utilization rate, 1/d; k is the first-order substrate removal constant, L/(mg·d); Ks is the half-saturation constant, mg/L.

The plots based on the experimental data and Eqs.(4) and (5) are shown in Fig.2, and the calculated kinetic parameters are shown in Tab.5.

Compared to the Blank, Y decreased by 42.8%, which indicated that excess sludge decreased when the same amount of substrate was degraded. At the same time, Kd decreased by 38.2%, which means that the microorganism activity increased. The biochemical reactions in both systems followed the first-order kinetics and the constant in the Tx-1 dosed system was 3.2 folds of the Blank. The kinetic parameters proved the good performance of the Tx-1 dosed activated sludge system.

2.5 Structure of microbial community

A different structure of microbial community was developed and a new balance in microbial community was established in the Tx-1 dosed system due to the selective and competitive growth of foreign and indigenous strains. It was observed that Acinetobacter, as a kind of representative model microorganism in the activated sludge system[18], had the highest abundance in the Blank system. After the addition of Tx-1, the Acinetobacter also appeared in high abundance (5.85%), but a different structure of microbial community appeared, as shown in Fig.3.

The abundance of polyphosphate accumulating organisms (PAOs) Comamonadaceae[19] and Tetrasphaera[20-21] increases from 3.24% and 1.31% to 11.53% and 3.39%, respectively, after the addition of Tx-1. The results show that more PAOs have colonized in the Tx-1 dosed system, and this may be one of the reasons for the enhancement of biological phosphorus removal.

The average Shannon indices of the TX-1 dosed and Blank systems are 4.58 and 4.32, respectively. According to the ecological principles, the higher the Shannon index, the greater the diversity, and the better stability and flexibility in the microbial community. That is to say, the Tx-1 dosed system has greater biodiversity, better stability and flexibility. So, the Tx-1 dosed system shows more resistance to the changes, including influent and operational conditions.

3 Conclusion

The multifunctional microbial agent Tx-1 is safe and convenient for the application in WWTPs. It can be introduced into the existing activated sludge process directly. Based on the full-scale study in A/O process, the addition of Tx-1 enhances the original A/O process. The Tx-1 dosed system obtains good effluent characteristics while minimizing sludge production and energy demand. The biological TP removal is enhanced in particular. The discharged dry sludge decreases by 64.3%; the air supply per cubic meter water reduces to 5.1 m3; and the electricity consumption reduces to 0.331 kW·h/m3. Based on the research in the laboratory, the addition of Tx-1 improves the first-order substrate removal constant and decreases the microorganism yield coefficient in the activated sludge process. The structure of the microbial community changes and the abundance of two kinds of PAOs increases. Tx-1 is a potential microbial agent in WWTPs for reducing excess sludge and enhancing phosphorous removal. In the future, a more effective microbial agent focusing on combining in-situ sludge minimization with pollutants removal should be developed.

[1]Pérez-Elvira S I, Nieto Diez P, Fdz-Polanco F. Sludge minimisation technologies[J]. Reviews in Environmental Science and Bio/Technology, 2006, 5(4): 375-398. DOI: 10.1007/s11157-005-5728-9.

[2]Hassani A H, Nejaei A, Torabian A. Excess sludge minimization in conventional activated sludge pilot plant by three chemical matters[J]. International Journal of Environmental Research, 2011, 5(4): 981-988.

[3]Uan D K, Yeom I T, Arulazhagan P, et al. Effects of sludge pretreatment on sludge reduction in a lab-scale anaerobic/anoxic/oxic system treating domestic wastewater[J]. International Journal of Environmental Science and Technology, 2012, 10(3): 495-502. DOI: 10.1007/s13762-012-0120-0.

[4]Yang S S, Guo W Q, Zhou X J, et al. Optimization of operating parameters for sludge process reduction under alternating aerobic/oxygen-limited conditions by response surface methodology[J]. Bioresource Technology, 2011, 102(21): 9843-9851. DOI: 10.1016/j.biortech.2011.07.079.

[5]Lou J Q, Sun P D, Guo M X, et al. Simultaneous sludge reduction and nutrient removal (SSRNR) with interaction between Tubificidae and microorganisms: A full-scale study[J]. Bioresource Technology, 2011, 102(24): 11132-11136. DOI: 10.1016/j.biortech.2011.09.048.

[6]Monica S, Karthik L, Mythili S, et al. Formulation of effective microbial consortia and its application for sewage treatment[J]. Journal of Microbial & Biochemical Technology, 2011, 3: 51-55. DOI: 10.4172/1948-5948.1000051.

[7]El K H M, El S S A, Ahmed D S, et al. Potential of effective microorganisms (EM) for conventional activated sludge upgrade[J]. International Water Technology Journal, 2013, 3(2): 78-87.

[8]Daiem M. Enhancing wastewater treatment by commercial and native microbial inocula with factorial design[J]. Life Science Journal, 2014, 11(7): 736-742.

[9]Szymanski N, Patterson R A. Effective microorganisms (EM) and wastewater systems[C]//Proceedings of On-site’03 Conference on Future Directions for On-site Systems: Best Management Practices. Armidale, Australia, 2003: 347-354.

[10]Li Mingzhi, Yu Zhiping, Chen Dequan, et al. Investigation on the application of microbial agents to environmental protection researches in China[J]. Industrial Water Treatment, 2011, 31(6): 18-20. (in Chinese)

[11]Zheng Hanling, Jiang Wei. Application status and precautions of bioaugmentation for in-situ sludge reduction[J]. Journal of Anhui Agricultural Sciences, 2014, 42(26): 9101-9103. (in Chinese)

[12]Li Mingzhi, Wei Yanfei, Mei Rongwu, et al. Field research on the application of multi-environmental microbial agent to sludge in situ decrement in biochemical systems[J]. Industrial Water Treatment, 2013, 33(2): 35-37. (in Chinese)

[13]Sumihar H D S, Setiadi T, Wenten I G. Kinetic study on the treatment of synthetic palm oil mill effluent by anaerobic membrane bioreactor (AMB)[J]. Jurnal Itenas, 2002, 1(6): 1-9.

[14]Shammas N K, Liu Y, Wang L K. Principles and kinetics of biological processes[C]//Advanced Biological Treatment Processes. New York, USA: Humana Press, 2009: 1-57.

[15]Grady C P L Jr, Daigger G T, Love N G. Biological wastewater treatment[M]. CRC Press, 2011.

[16]Pittoors E, Guo Y, Hulle S W H V. Modeling dissolved oxygen concentration for optimizing aeration systems and reducing oxygen consumption in activated sludge processes: A review[J]. Chemical Engineering Communications, 2014, 201(8): 983-1002. DOI: 10.1080/00986445.2014.883974.

[17]Liu G Q, Wang J M. Modeling effects of DO and SRT on activated sludge decay and production[J]. Water Research, 2015, 80: 169-178. DOI: 10.1016/j.watres.2015.04.042.

[18]Stroot P G, Hoessle A R, Oerther D B. Microbial succession in activated sludge: Ecological principles link community diversity and operating performance[C]//Proceedings of the Water Environment Federation. Water Environment Federation, 2001: 772-779. DOI:10.2175/193864701790902482.

[19]Ge H, Batstone D J, Keller J. Biological phosphorus removal from abattoir wastewater at very short sludge ages mediated by novel PAO clade Comamonadaceae[J]. Water Research, 2015, 69: 173-182. DOI: 10.1016/j.watres.2014.11.026.

[20]Yuan Z, Pratt S, Batstone D J. Phosphorus recovery from wastewater through microbial processes[J]. Current Opinion in Biotechnology, 2012, 23(6): 878-883. DOI:10.1016/j.copbio.2012.08.001.

[21]Muszynski A, Milobedzka A. The effects of carbon/phosphorus ratio on polyphosphate-and glycogen-accumulating organisms in aerobic granular sludge[J]. International Journal of Environmental Science and Technology, 2015, 12(9): 3053-3060. DOI: 10.1007/s13762-015-0828-8.

微生物菌剂在线污泥减量的生产性应用研究

谢慧芳1 张晋华1 辛文力1 胡灿洋1 严梅1 张青1 贺启环1 周建成2

(1南京理工大学环境与生物工程学院, 南京 210094)(2东南大学化学化工学院, 南京 211189)

摘要：在A/O污水处理线上开展了为期8个月的投加多功能菌剂Tx-1的生产性应用试验.结果表明:菌剂的投加明显提高了水处理效果,同时减少了污泥产量,降低了能量消耗.在不投加化学除磷剂的情况下,出水总磷含量低于0.5 mg/L;万吨水外排绝干泥量Dwat由1.4 t下降到0.5 t;处理每立方米水所需曝气量由6.0 m3下降到5.1 m3;处理每立方米水的电耗由0.412～0.425 kW·h下降至0.331 kW·h.投加Tx-1可以提高活性污泥系统的一级基质去除速率常数,降低污泥产率系数.同时投菌体系中的活性污泥菌群结构发生了变化,生物多样性增加;其中2种聚磷菌Comamonadaceae和Tetrasphaera的丰度明显增加.有效的微生物菌剂可为实现在线污泥减量及污染物去除提供解决途径.

关键词：污水处理;投菌A/O工艺;微生物菌落多样性;动力学参数

Foundation item：The Natural Science Foundation of Jiangsu Province (No.BK20151485).

Citation：：Xie Huifang, Zhang Jinhua, Xin Wenli, et al. Full-scale application of microbial agent on in-situ sludge reduction[J].Journal of Southeast University (English Edition),2016,32(4):502-507.

Biography：Xie Huifang (1972—), female, doctor, associate professor,huifanxie@hotmail.com.