Study on Aerobic Composting of Mixed Municipal Sludge Kitchen Waste and Water Hy

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Abstract. In this study， a in vessel aerobic composting method is adopted to investigate the variation rules of various evaluation parameters （temperature， moisture content， pH， organic matter， water soluble ammonia nitrogen， water soluble nitrate nitrogen and germination index） in co-composting of municipal sludge， kitchen waste and water hyacinth at different proportions. The results show that， in composting， the parameters of moisture content， pH， water soluble ammonia nitrogen and water soluble nitrate nitrogen demonstrate marked dynamic change rules during composting process； the temperature of three groups of compost materials rapidly rise to above 55 ℃ within 96h， and last for 3 ～ 7d， meeting the harmless requirements， and their organic matter degradation rate excess 30%， the GI index is higher than 83%， in line with the requirements on maturity， which proves that the co-composting of municipal sludge， kitchen waste and water hyacinth can realize harmlessness and resource reutilization after composting.

Key words： sewage sludge； kitchen waste； water hyacinth； aerobic composting

The influence of kitchen waste on environmental quality is denounced by public all the time. In recent years， with the exposure of swill-fed pigs and hogwash oil， the kitchen waste attracts widespread attention of social public， and is in urgent need for reasonable treatment [1]. Water hyacinth， with eichhornia crassipes as its scientific name， is one of the perennial aquatic weeds with fastest growth， fastest reproduction and the most serious harm， which has been widespread and uncurbed in more than ten provinces in south of our country [2，3]. At the meantime， the municipal sludge has high yield， and the treatment and disposition thereof become a hot problem of municipal environmental protection [4]. Sludge disposition includes lots of methods such as landfill， incineration， resource utilization and the like， while the resource utilization is the main development tendency for solving problems of sludge due to gradually shorter supply of land and potential environmental pollution risk [5].

Resource utilization can be realized by composting the municipal sludge， but the sludge has high moisture content and low porosity， so auxiliary materials shall be added for regulation in composting. The water hyacinth has abundant fibers [6]， and the kitchen waste has high organic matter content as well， so by adding the kitchen waste and the water hyacinth into the municipal sludge for composting， on one hand， the structure and moisture content of the composting materials can be regulated， and on the other hand， recycling disposition of the kitchen waste and the water hyacinth can be simultaneously achieved as well.

1. Materials and method

1.1 Experimental materials

（1）Composting facility

This experiment adopts vertical ventilation and horizontal air supply.

The composting facility adopted in the experiment is shown in Figure 1. The composting facility consists of a composting layer and a water collection and air distribution layer， and is made of a stainless steel plate that is 8 mm in thickness， wherein the volume of the composting layer is 300×300×500 mm3， and three inspection sampling holes are arranged from the top down along the bin body. A ventilating perforated pipe is arranged in the composting layer， and a vent of 3 mm in diameter is opened in the pipe. To prevent the percolate generated by composting from blocking the air outlet， immersing composting materials and resulting in the anaerobic condition at the bottom of the composting material， the funnel-shaped water collection and air distribution layer is arranged below the composting layer， and it is provided with a horizontal air outlet pipe and a vertical water outlet pipe. A high-intensity PVC clapboard with holes is arranged between the composting layer and the water collection and air distribution layer， and small holes with an aperture of 8 mm are uniformly distributed at an interval of 22 mm on the clapboard. The gases generated by forced ventilation and reaction and the percolate generated in composting are discharged to the water collection and air distribution layer via the clapboard and then respectively discharged from the composting facility via the air outlet pipe and the water outlet pipe.

（2） Ventilating device

The ventilating device adopted in the experiment is an electromagnetic air compressor. The ventilation frequency and ventilatory capacity are respectively controlled by a time controller and a glass rotor flowmeter. Ventilating pipelines are connected by hoses into the composting facility through the air inlet hole in the upper part of the self-reactor. The ventilating device and the air paths are specifically shown in Figure 2.

（3） Composting raw materials

The municipal sludge used in the experiment comes from the dewatered sludge processed in the second-stage project of the Guangzhou Liede Sewage Treatment Plant. The kitchen waste used in the experiment comes from the Juyuan restaurant of Sun Yat-Sen University， including hogwash and kitchen garbage. After sampling， the samples are manually sorted to remove non-compostable parts such as glass and plastic， and are crushed to grains sized smaller than 50 mm. The water hyacinth used in the experiment is refloated from the water channel near to the Guangzhou Yingzhou Ecological Park， and before composting， the samples are manually sorted， separated from soil， cleaned， dried in the sun， and crushed.

1.2 Experimental method and sampling

The experiment mainly includes three experimental steps of composting material pretreatment， primary fermentation and secondary fermentation. The composting material pretreatment mainly includes： crushing kitchen waste and water hyacinth， regulating the particle size， mixing the municipal sludge with kitchen waste， respectively adding water hyacinth， regulating the C/N value and the moisture content. The primary fermentation is implemented in the closed composting facility， and the secondary fermentation adopts open-air composting and natural ventilation.

Three groups of experiments are performed in total， with each group divided into three compost bodies A， B and C according to different ventilation quantities and material ratios in the composting design. The ratio and ventilation conditions of the composting materials are shown in Table 2：

Sampling time and method： Sampling analysis is carried out respectively on 0th day，2nd day， 4th day， 7th day， 11th day， 15th day， 20th day， 26th day， 33rd day， 32nd day and 50th day in composting. In sampling， the samples are taken from a plurality of points in the upper， middle and lower sampling openings respectively， mixed and then reduced to about 100g.

1.3 Sample analysis method

Temperature measurement time and method： The temperature is measured twice every day， respectively at 9 am and 5 pm. During measurement， the temperature of the three sampling openings is measured by the mercurial thermometer， and the mean value is taken. In the primary fermentation， the temperature is measured every day， and during sampling in the secondary fermentation， the temperature of the sample is measured and the room temperature of every day is recorded.

2. Results and discussion

（1） Temperature variation

As one of the important factors in composting， the temperature influences the quality of composting products. As shown in Figure 3， the environmental temperature of this experiment is kept above 15℃ all the time， and each compost body goes through a temperature rise period， a high temperature period and a stable period in aerobic composting[10]， but the compost bodies are slightly different in temperature rise rate and high temperature duration time. In experiments A and B， the temperature rises rapidly， respectively taking 96h and 105h to rise from the room temperature to the highest temperature ， with temperature rise rates of 0.385℃/h and 0.375℃/h respectively. The duration time of the high temperature above 55℃ is respectively 3d and 4d. The temperature rise rate is 0.328℃/h in experiment C， which is a little slower， but the duration time of the high temperature above 55℃ in this compost body is as long as 7d. The high temperature duration time of each group of experiments can reach the standard provided by the USA Environmental Protection Agency that the high temperature above 55℃ must be continued for more than 3d. After the high temperature period is ended， each compost body is taken out of storage at the 11th day for secondary fermentation； and after each compost body is taken out of storage， the temperature is reduced rapidly and reduced to the room temperature at the 20th day.

The three groups of experiments show that： with the same ventilation quantity but different material ratios， the compost bodies are different in temperature rise rate as well. The possible reasons may be that： in experiments A， B and C， the content of the sludge in the composting materials is orderly increased， the content of the kitchen waste is orderly reduced， and the porosity satisfies that： A> B>C. In experiment A， the composting material has high kitchen waste content and large porosity； the pores are full of oxygen in beginning of composting， which contributes to the increase of the activity of microorganisms， but heat will be taken away by continuously-inhaled air in large-porosity environment， resulting in rapid temperature drop of the composting material. The sludge contains a great quantity of microorganisms； in experiments B and C， the quantity of microorganisms increases with increment of the sludge quantity， and the porosity is smaller when the sludge is more， and the activity of the microorganisms is gradually improved after air is inhaled.

（2） Variation of moisture content

As shown in Figure 4， at the beginning of composting， the moisture contents of A， B and C are respectively 53.7%， 54.1% and 52.0%. The moisture contents of the three groups of experiments go through a rise period in the initial stage of composting and then obviously drop. In the secondary fermentation stage， the moisture contents are reduced to 9%-10% and tend to be stable. The three groups of experiments are the same in variation tendency of the moisture content， and the moisture content is reduced by more than 80%. The moisture content has a short rise process in the initial stage of composting， and the causes may be as follows： temperature rise causes activity improvement of mesophilic microbial community and thermophilic microbial community， lots of organic matters are degraded by effects of the microorganisms， water will be generated by oxygenolysis of the organic matters and breathing effect of microorganisms， while the temperature rise of the compost body also causes leakage of water in the clearances of the compost materials and the internal water of microorganism cells. At the beginning of composting， the temperature of the compost body is in the rise stage， and the composting material has low water volatile content. The moisture content is higher when the water volatile content is smaller than the generated moisture content.

（3） Variation rule of pH

In this experiment， the initial pH values are within 6.72-7.32. According to the variation condition of the pH in composting， at the 2rd day of composting， the pH drop to minimum， respectively 6.71， 6.74 and 6.02， thereafter the pH are in gradually rising trend， successively reach the maximum between the 7th to the 11th day， then start to drop； fluctuation occurs in the secondary fermentation period， and finally is stabilized between 7.21-7.38.

In the three groups of composting experiments， the pH have the same variation trend： dropping at first， rising to the maximum and then gradually dropping to be stable. At the beginning of composting， organic acid is generated when the microorganisms are decomposing the organic matters， resulting in drop of the pH， and the pH starts to rise with the process that the organic acid is further decomposed to be CO2 and water. At the meantime， ammonium nitrogen substances will be generated when the microorganisms decompose nitrogenous organics， and the volatilization of the ammonia gas in high temperature environment also causes rise of the pH in the compost body. After the high temperature stage of composting is ended， most of the labile organism matters in the compost body are degraded by the microorganisms； the activity of thermophilic microorganisms is restrained， the mesophilic microorganisms continue to grow and reproduce， the activity of nitrobacteria is improved， H+ is generated by nitrification， and in addition， the ammonia gas is lost due to volatilization， which causes drop of the pH of the compost body. Thereafter， the temperature of the compost body drops， humus is continuously generated and the temperature basically reaches a stable state； the composting enters the ageing stage， and the pH tends to be stable.

（4） Variation rule of organic matter

In this experiment， the value of the organic matter takes 1.73 times the TOC value. As shown in Figure 6， the content of the organic matter is gradually reduced with proceeding of composting. The contents of the organic matters are respectively reduced from the initial values of 65.5%， 65.1% and 66.9% to 43.3%， 44.5% and 44.2% at the end of composting.

The degradation of the organic matters takes place mainly in the primary fermentation stage； content variation of the organic matters in the secondary fermentation stage is small， and the organic matters are basically stable in content at the later stage of composting.

（5） Variation rule of water soluble nitrate nitrogen （WS-NO3--N）

The variation rule of the water soluble nitrate nitrogen is shown in Figure 7. During the whole composting process， the concentration of the water soluble nitrate nitrogen is in rise trend. In the primary fermentation stage， the nitrate nitrogen has small concentration variation， mainly because that the activity of the nitrobacteria is restrained in this stage， and nitrogenous organic matters exist as water soluble ammoniacal nitrogen. In the secondary fermentation stage， the temperature gradually drops， the activity of the nitrobacteria is gradually improved， and the concentration of the nitrate nitrogen is remarkably increased by nitrification and finally reaches about 400 mg/kg.

（6） Variation rule of water soluble ammoniacal nitrogen （WS-NH4+-N）

During composting， the form and concentration variation rule of ammonia are influenced by degradation rate of nitrogenous organic matters in the compost body in the primary fermentation stage. In the initial stage of composting， microorganisms grow and reproduce well， the temperature rises rapidly， and the form of ammonia changes with the temperature rise. As shown in Figure 8， in the primary fermentation stage， the concentration of NH4+-N in each compost body sharply rises； intense mineralization causes rapid degradation of nitrogenous substances by microorganisms， simultaneously generation of a great number of organic acid causes drop of the pH value， and the decomposed nitrogen exists in the form of water soluble ammoniacal nitrogen. The initial concentration of NH4+-N is 1204.7～1751.6mg/kg and rises to 2735.9～3553.1mg/kg after 7 days. After the high temperature stage， the activity of microorganisms is reduced， the pH value rises， NH4+-N escapes in the form of ammonia gas or is dissolved in the percolate， thus resulting in that the loss amount thereof is larger than ammoniation of microorganism， and the content of the water soluble ammoniacal nitrogen is gradually reduced.

In the secondary fermentation stage， the rest nitrogenous organic matters in the compost body continue to be degraded. The activity of the nitrobacteria is improved when the temperature drops below 40℃， and NH4+-N is transformed into nitrate nitrogen， resulting in drop of the content of NH4+-N. With enhancement of nitrification and reduction of the nitrogenous organic matters， the concentration of the water soluble ammoniacal nitrogen is gradually reduced and finally stays stable at 776.4～900.6 mg/kg. The water soluble ammoniacal nitrogen has an toxic action on plants， Li Chengqiang et al [11] proposed that when NH4+-N is used as an evaluation index of putrescibility of the composting process， the concentration of NH4+-N in ageing composting shall be within the range of 500 ～1400 mg/kg， and the concentration of the water soluble ammoniacal nitrogen of the composting product in the experiment is within this range.

（7）） Variation rule of seed germination index （GI）

Figure 9 shows the variation rule of the seed germination index （GI） in this experiment. The comparison shows that the GI before composting is quite low， within 19.65%～25.92%， and is within 83.54%～89.89% after composting， which proves that composting can realize harmlessness of the sludge， the kitchen waste and the water hyacinth. Generally， the compost is considered to be basically nontoxic if Gi is larger than 50%， and it is totally aged while GI is larger than 80%. In this composting experiment， at the 26th day in composting， the GI of each group of experiments is above 50%， and it is above 80% at the 45th day in composting.

In the experiment， the GI has three stages： the period from the 2rd day to the 7th day in composting is the sprout inhibition stage in which the minimal value of the GI is close to 0； then the rise stage of the GI， in which the GI slowly rises at first， then rapidly rises at the 15th-33th days to enter the ageing stage and finally stays in a slowly rising to stable stage. The main causes are： a great number of substances that are toxic to plants， such as organic acid and ammoniacal nitrogen， are generated in the primary fermentation period， resulting in drop of the GI； in the secondary fermentation period， the organic acid is decomposed to be CO2 and water， the ammoniacal nitrogen is transformed into nitrate nitrogen by nitrification， the toxicity to plants is reduced， and GI rises rapidly.

3. Conclusion

（1） In the three groups of experiments of the mixed materials of the municipal sludge， the kitchen waste and the water hyacinth， the temperature in each experiment rapidly rises to above 55℃ within 96h and is continued for 3-7 days， and the high temperature duration time meets the harmless treatment requirements of the compost body.

（2） The three groups of experiments basically have the same index variation rule of moisture content， pH value， NO3--N， etc. The degradation rate of the organic matters in each group of experiments is higher than 30%， and the organic matters are effectively degraded.

（3） Both the concentration of NH4+-N and the GI can be used as putrescibility indexes in composting. In the experiments， the concentration of the water soluble ammoniacal nitrogen of the composting product is within the range of 500 ～1400 mg/kg， all the GI values are higher than 80%， and good ageing degree is achieved in composting， which proves that aerobic composting can realize harmlessness and resource utilization of the mixed materials of the municipal sludge， the kitchen waste and the water hyacinth.

Acknowledgement

Supported by Foundation for the Cooperation of Industry， Education and Academy of Guangdong Science and Technology Department of China（2010B090400418）

References

[1] Yan Difei， Kitchen Garbage Standard Management Research， Environmental Science and Technology， 2010，Vol.23， Supp.2：89-92

[2]Jiang Hongtao， Zhang Hongmei， Home and Abroad Water Hyacinth Prevention and Treatment Research Summary， China's Agricultural Science and Technology Riview， 2003， 5 （3 ）： 72-75.

[3] Holm LG， Plucknett D L， Pancho JV， et a1. World’s Worst Weeds Distribution

and Biology. Honolulu： The Univers ity Press of Hawaii. 1： 609.

[4] Li Biqing， Tang Yao， Feng Xin， etc. Guangzhou Municipal Sludge Treatment Method. Environment Engineering， 2011， （Z1）： 220-222.

[5] Municipal Sludge Resource Utilization Situation and Development Discussion， 2013， Vol.11， No.2：99-103. 12

[6] Yu Youcheng， Nutritional Ingredient and Silage Method of Water Hyacinth. Feed china， 1988 （2）： 38-41.

[7] State Environmental Protection Administration Water and Waste Water Monitoring Analysis Method Editorial Committee. Water and Waste Water Monitoring Analysis Method （The Fourth Edition）. China Environmental Science Press， 2002.

[8] Bao Shidan， Soil Agrochemistry Analysis （The Third Edition）. China Agriculture Press， 2000.

[9] Chen Lingyun， Measure Heavy Metals in Municipal Sludge by Plasma Emission Spectroscopy. Chemical Analysis and Meterage， 2008， 17 （3）： 39-41.

[10] Zhu Xiaoshan， Yu Fanping. Zhao， Xijin. Treatment Technology and Resource Utilization Prospect of Municipal Sludge. Environment of Sichuan， 2002， 21 （4）： 8-12.

[11] Li Chengqiang， Wei， Yuansong， Fan， Yaobo， etc. Property Variation and Putrescibility of Aerobic Composting of Different Filler Sludge. Environmental Science， 2001， 22 （3）： 60-65.