original article accelerated stabilization of landfill in a high … · original article...

Int J Clin Exp Med 2016;9(2):5218-5227www.ijcem.com /ISSN:1940-5901/IJCEM0015800

Original ArticleAccelerated stabilization of landfill in a high-latitude area by EM and a risk assessment to human health

Yang Song, Huiling Liu

School of Municipal and Environmental Engineering, Harbin Institute of Technology, No. 73 Huanghe Road, Har-bin 150090, China

Received September 7, 2015; Accepted December 5, 2015; Epub February 15, 2016; Published February 29, 2016

Abstract: The leachate from post-closure landfill can potentially do great harm to human health via physical and chemical reactions if it has not been properly treated. In this study, we provide an effective method for accelerat-ing the stabilization of enclosed landfill and biodegrading the toxic compounds in the leachate by using effective microorganisms (EM). The human health risk of toxic components in leachate was also analyzed and evaluated us-ing water environmental health risk assessment models. The results show that the landfill compost was stabilized within 12 days. The concentrations of the carcinogenic and non-carcinogenic chemicals after biodegradation with EM were significantly decreased.

Keywords: Landfill, effective microorganisms, compost, leachate, human health risk

Introduction

Due to the low temperatures of the long winter in northeast China, landfill in these areas can only be stabilized after 17 to 19 years of natu-ral degradation [1]. During long-term stabiliza-tion, the groundwater, surface water and soil can become severely contaminated by hazard-ous materials in the landfill, such as organic compounds and heavy metals [2-5]. The toxic components in leachate from post-closure landfill can be extremely hazardous to both the environment [6-8] and human health [9]. Th- erefore, the acceleration of stabilization of landfill is very important for the control of pollu-tion and the ecological remediation of the area surrounding the landfill site. Effective Mic- roorganisms (EM) are complex micro ecological agents, including 5 families of bacteria (such as lactic acid bacteria, yeasts, Actinomycetes, and photosynthetic bacteria), 10 genera, and more than 80 species of bacteria. EM was first investigated by Professor Teruo Higa in Japan, and has been applied in agriculture, aquacul-ture, and environmental protection since 1992. The different principles involved in EM com-posting versus traditional composting are as follows: organic matter in landfill is naturally oxi- datively decomposed by microorganisms when

a traditional composting method is employed; in contrast, for EM composting, the decomposi-tion of organic matter in landfill is a fermenta-tion process with yields of ammonia, hydrogen sulfide and methane that can serve as nutrients for EM to support their metabolism [10]. The cri-teria for stabilization, the environmental impact, and the operation of the composting of landfill have been reported in many previous papers. In general, researchers focused their attention on the installation of composting experimental set-ups and comparisons of the biodegrada-tion efficiencies of landfill with different biore-actors. However, the treatment of landfill still needs to be further investigated [11, 12]. In- tensive studies on biodegradation of municipal waste, especially the treatment of landfill with EM, are required.

The objectives of the present research were to investigate the feasibility of accelerating the stabilization of landfill by using EM to neutralize toxic components, and to make a risk assess-ment of leachate from a post-closure landfill site. In this study, the municipal solid waste from landfill in Northeast (China) was thorough-ly biodegraded by the addition of EM. The EM treatment in this study was used to determine unequivocally whether stabilization and degra-

EM stabilization of high-latitude area landfill and a risk assessment to human health

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dation of toxic components in leachate would occur, and how beneficial the treatment is for the recovery of the ecological function of leach-ate polluted water and soil. The concentrations of carcinogenic substance (including Cd and Cr6+) and non-carcinogenic chemicals (such as Pb, Hg and NH3) in municipal solid waste before and after EM treatment were analyzed.

Materials and methods

Experimental plot

The landfill and its surroundings are shown in Figure 1A. This landfill, which was built in 1997 and enclosed in 2006, occupies an area of 120,000 m2 with a height of 0.8-7.1 m and a volume of 1,000,000 m3. According to explora-tion of the geomorphology, the landfill site is located in the floodplain of an urban river, and is composed of cohesive soil and sandy soil formed during quaternary sedimentation. As shown in Figure 1B, the experimental plot is 25 m2 and divided into 4 composting areas.

Experimental materials

EM was provided by the Research Institute of Biological Engineering (Harbin, China), of which 120 kg was used in the present study. Sixteen tons of municipal solid waste was taken from the post-closure landfill.

EM composting method

The solid waste from the landfill was divided into 8 samples, each of which weighed 2 tonnes. EM (0 kg, 1 kg, 2 kg, 5 kg, 10 kg, 15 kg, 20 kg, and 30 kg was added to each sample, respectively. The ratio of EM to solid waste was 0-15%. Within 4 weeks, the temperature of the EM compost was controlled between 20°C and 60°C [13], and the humidity was in the range 60%-70% [14]. The EM compost was mixed every 6 h. In order to protect the compost from rain, experiments were conducted inside a waterproof fermentation chamber, with a drain-age system to prevent the samples from be- ing drenched by rain and other pollutants. The parameters of the EM compost (including inner temperature, biological degradable materi-al (BDM), and organic matter) were measured every 12 h for the first 2 days, and once every 48 h from day 3. The fermentation experiments were successively carried out in July and Au- gust. The carcinogenic chemicals and non-car-cinogenic chemicals of leachate were analyzed after 4 weeks of biodegradation treatment with EM.

Characterization of organic matter changes measured by 3-D excitation-emission matrix fluorescence spectrometry (3DEEM)

All samples were pre-treated as follows: first, samples were dissolved with deionized water in

Figure 1. Map of the landfill used in the present research (A) and experimental plot of EM compost used in this research (B). (2000=2 meter).


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a triangular bottle. The weight ratio (g/g) of sample to deionized water was 1 to 1; second, the mixed solution in the bottle was shaken at a rotating speed of 200 r/min at constant tem-perature for 16 h, followed by centrifugation separation at 4,000 r/m for 30 min; third, the supernatant was filtered with a 0.45 μm sterile microporous membrane. The filtrate was stored in a dark place to avoid the effects of light at 4°C.

Analytical methods

The solid waste from landfill was dried in an oven at 105°C until a constant weight was achieved. Contaminating inorganic waste (such as metal, stones and glass) and organic waste (including non- degradable rubber and plastic) were separated from the dried samples. Then, the samples were ground in a ball grinder for 6 h and screened with a 20-mesh sieve before they were analyzed.

As defined by the National Academy of Sciences, America, public health risk assessment is the disadvantage to human health when the human body is exposed to environmental hazardous factors [15]. According to the overall assess-ment of carcinogenic chemicals by the World Health Organization (WHO) and the International Agency Research on Cancer (IARC), the health risk caused by hazardous materials can be divided into two categories, namely a carcino-genic chemical human health risk and a non-carcinogenic human health risk [16, 17]. Th- erefore, in the present study the toxic pollut-ants in municipal solid waste have been classi-fied into carcinogenic chemicals (including Cd and Cr6+) and non-carcinogenic chemicals (including Pb, Hg, and NH3).

Risk of carcinogenic chemicals on human health

The human health risks of carcinogenic chemicals were assessed by using the following model [18]:

RR igcc

1i

k

==

/ (1)

[1 exp ( )] /70R D qigc

ig ig= - - (2)

where Rigc is the average individual carcinogen-ic risk per year of k kinds of carcinogenic chemi-cals via ingestion per year (a-1); Dig is the indi-vidual exposure dose of carcinogenic chemicals

via ingestion per unit weight everyday (mg/(kg·d)); qig is carcinogenic strength factor of carcinogenic chemicals via ingestion (mg/(kg· d)); 70 (years) represents the average longevity of the human life span (a). The Dig via water intake was calculated as follows:

2.2 ( ) /70D C xig i= 9# (3)

where 2.2 is an individual’s water intake vol-ume per day (L); ( )C xi is the average increase in concentration per year (mg/L); 70 is the aver-age individual weight (kg).

Risk of non-carcinogenic chemicals to human health

The risk of non-carcinogenic chemicals to human health was calculated according to the following equation model [18]:

10 / /R R , R (D RfD ) 706

1

nign

ign

ig

i

l

ig= = # -

=/ (4)

where i is non-carcinogenic pollutant, Rign

is the average individual risk of non-carcinogenic pol-lutant on human health per year via ingestion (a-1); Dig is the exposure dose of non-carcino-genic pollutants individually through ingestion per day (mg/(kg·d)); RfDig is the relevant intake dose of non-carcinogenic pollutants after ingestion (mg/(kg·d); 70 (years) represents the average longevity of the human life span (a). Based on the assumption that risk and hazard caused by every chemical affects on human health separately without internal synergistic reaction among them, the entire hazard to human health can be calculated as follows:

R R RTotalc n= + (5)

where RTotal is the entire human risk of non-car-cinogenic pollutants.

Results and discussion

Effects of EM on the temperature of the com-post

The temperature variations of the EM compost are shown in Figure 2A and 2B, which shows that the external temperatures of the EM com-post were maintained at >20°C in July and between 12°C and 26°C in August, while the inner temperature of the EM compost ranged from 20°C to 35°C in July and from 22.5°C to 35°C in August. The EM compost temperature reached a maximum after 2 days in July and


5221 Int J Clin Exp Med 2016;9(2):5218-5227

after 4 days in August, and then steadily decreased. As shown in Figure 2A and 2B, the temperature of the EM compost fluctuated with changes in the external temperature of the compost during the day and night. Especially in August, the temperature decreased to 15-20°C, regardless of the day or night-time, but the tem-perature of the EM compost was still main-tained at >25°C. Finally, it is noteworthy that the temperature of the EM compost was rela-tively constant after stabilization of the landfill samples.

In addition, when the fermentation of municipal solid waste with EM was carried out in a high latitude area, the temperature change of both the internal and external compost was different to that of the compost studied in a laboratory within a reactor. For the compost conducted in a reactor, the temperature increased with time until it reached a maximum value. In contrast, and fairly obviously, when the fermentation of solid waste was conducted outdoors the com-posting temperature was affected by the out-side ambient temperature.

Figure 2. Changes in inner and external temperatures (A, B), in BDM content (%) (C, D) and in the organic matter content (%) (E, F) of EM composts with different EM concentrations sampled in July 2011 (A, C, E) and August 2011 (B, D, F).


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Effects of EM on the BDM content of compost

The background level of soil organic matter content in Northeast China ranges from 2% to 7% [19], while the background levels of BDM ranges from 2% to 5%. Therefore, the stabiliza-tion of solid waste from landfill could be identi-fied when the BDM content and organic matter content were less than 5% and 7%, respectively.

The effects of EM on the BDM content of com-post are shown in Figure 2C and 2D and Table 1. Inspection of the data reveals that degrada-tion of BDM was accelerated when EM was added to the compost. The highest biodegrada-tion efficiency of BDM was obtained when 20 kg of EM was added to 2 tonnes of solid waste. Thus, the results indicate that the optimal EM dosage for achieving effective acceleration of solid waste stabilization is 1% hyperthermal EM bacteria (i.e. 20 kg bacteria) for every 2 tonnes of municipal solid waste. The results al-

decrease in BDM content progressively declined.

Effects of EM on the content of organic matter in municipal solid waste

The organic matter content in EM compost was measured in July 2011 and August 2011, respectively and the results are shown in Figure 2E and 2F and Table 2. The addition of EM was clearly beneficial to biodegradation of the organic matter, indicating that stabilization of solid waste from landfill was accelerated after the addition of EM. Compared with other EM concentrations, the organic matter content was decreased most rapidly when 20 or 30 kg of EM was added into two tonnes of solid waste. Thus, it can be concluded that the EM dosage for fermentation of compost was optimized at 1-1.5% hyperthermal EM (i.e. 20-30 kg EM) for every 2 tonnes of solid waste from landfill. In addition, the results also revealed that the bio-degradation efficiency of solid waste is >70%

Table 1. Comparison of BDM content (%) of EM compost before and after fermentation with EM

BDM content2011

July AugustIn-pile EM concentration

Before treatment

After treatment

Decline level

Before treatment

After treatment

Decline level

1 kg 31.75 23.89 24.76% 29.31 25.46 13.14%2 kg 30.21 19.77 34.56% 29.33 20.1 31.47%5 kg 29.72 11.13 62.55% 28.17 12.87 54.31%10 kg 32.54 9.9 69.58% 27.06 13 51.96%15 kg 31.75 8.07 74.58% 27.27 6.92 74.62%20 kg 32.53 5.07 84.41% 28.96 5.03 82.63%30 kg 3191 4.88 84.71% 28.07 4.87 79.98%

so show that the biodegrada-tion efficiency is >80% within 14 days after 1% EM was added to the solid waste. Later, the BDM content tend-ed to be constant, which indi-cated that the BDM level in the municipal solid waste was stabilized.

It is noteworthy that there was little change in the BDM con-tent after 1 kg of EM was added to the compost for 14 days. By contrast, remarkable changes occurred in the in-pile BDM content with other EM concentrations. In the ea- rly stages of the experiment, there was little change in the in-pile BDM content during th- e first 4 days, which is attrib-uted to the fact that the micro-organism would have been in the adaptive phase. The rapid proliferation of microorgan-isms resulted in a dramatic decline of the BDM content after the adaptation period. The highest biodegradation efficiency of BDM was achieved on day 4, after which the

Table 2. Comparison of organic matter contents (%) of EM compost before and after fermentation with EMOrganic matter

2011July August

In-pile EM concentration

Before treatment

After treatment

Decline level

Before treatment

After treatment

Decline level

1 kg 23.19 10.63 54.16% 23.37 0.87 53.49%2 kg 24.74 11.12 55.05% 22.48 11.38 49.38%5 kg 22.63 9.82 56.61% 23.77 9.61 59.57%10 kg 23.47 8.33 64.51% 21.91 8.52 61.11%15 kg 24.33 7.65 68.56% 24.08 7.73 67.90%20 kg 23.44 6.26 73.29% 22.18 6.44 70.96%30 kg 24.13 6.15 74.51% 23.59 6.25 73.51%


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when 1-1.5% EM was added within 12 days. Furthermore, the organic matter content was

decreased to 6.2% after 14 days of fermenta-tion composting when 1.5% EM was added to

Figure 3. 3DEEM patterns for DOM fractions in a blank sample before EM fermentation treatment (A) and in solid waste samples after EM fermentation treatment with different EM additions: (B) 0.5 kg, (C) 1 kg, (D) 2 kg, (E) 5 kg, (F) 10 kg, (G) 15 kg. (B-E) Show the 3DEEM patterns of samples diluted 10 times. (F, G) Show the 3DEEM patterns of samples diluted 100 times.


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the field experiment system, resulting in stabili-zation of the solid waste. The variation in BDM and organic matter concentration with time is in agreement with the results obtained using a fermentation reactor. The concentrations of BDM and organic matter declined gradually until they reached stable points.

Effects of EM on organic matter in solid waste

The 3DEEM of DOM components in solid waste before and after EM treatment are shown in Figure 3. The fluorescence peaks a-d reflect proteins [20-22], fulvic-like material, microbial metabolites [23], and humic-like material [24], respectively.

As shown in Figure 3A, the major component of municipal solid waste before EM treatment were protein (a region) and microbial metabo-lites (c region), while the minor component was humic-like material (d region). Figure 3B-G show that the protein (a region) and microbial metabolite (c region) component contents were obviously decreased after EM treatment; how-ever, the component content of humic-like material (d region) was significantly increased. No obvious change in the fulvic-like material content (b region) was found before and after EM treatment. In summary, the EM fermenta-tion treatment was beneficial for the biodegra-dation of protein and increased the humic-like material content.

Human health risk assessment of landfill leachate before and after EM treatment

The concentrations of carcinogenic (Cd, Cr6+) and non-carcinogenic (Pb, Hg, NH3) chemicals in leachate before and after EM treatment are shown in Table 3.

after EM biodegradation were 5.4×10-6/year and 4.6×10-6/year in July 2011 as well as 7.610-6/year and 3×10-6/year in August 2011. The results indicate that the human health risk of Cd was decreased by 15.14% in July and by 59.92% in August 2011 after EM treatment. For Cr6+, the human health risk was decreased from 2.9602×10-4/year to 4.668×10-5/year by 84.2% in July and from 2.9728×10-4 to 3.3831×10-5 by 88.62% in August 2011. The remaining average population risks for Cd and Cr6+ were 4.6 person/(million person/year) and 46.68 person/(million person/year) in July as well as 3 persons/(million person/year) and 33.83 persons/(million person/year) in August 2011 after EM treatments.

Table 4 shows that the human health risks of non-carcinogenic chemicals in solid waste fol-lows the order Pd > Hg > NH3 (Figure 4) and Pb and Hg were the main pollutants in solid waste; Pb reductions were about 2.5-4.5 higher than for Hg (Table 4). Figure 5 shows that the total human health risk of carcinogenic chemicals was decreased by 82.9% after EM fermenta-tion in 2011 July, and that the non-carcinogenic chemicals declined by 73%. In August 2011, the human health risk of carcinogenic chemi-cals per year decreased by 87.9% after EM treatment, while that of non-carcinogenic chemicals decreased by 87.8% after biodegradation.

Heavy metal pollution in China has become an increasing problem during the last decades [25] and the annual total volume of discharged heavy metals into waste water, waste gas and solid wastes was about 900,000 tonnes between 2005-2011 [26]. In case of free avail-ability in the soil the heavy metals are up taken

Table 3. Chemical concentrations in leachate before and after EM treatment (mg/L)Carcinogenic/non-carcinogenic July 2011 August 2011

Pollutants Before treatment

After treatment

Before treatment

After treatment

Cd 1.980×10-3 1.68×10-3 2.77×10-3 1.11×10-3

Cr6+ 1.625×10-2 2.54×10-3 1.632×10-3 1.84×10-3

Pb 2.733×10-1 2.507×10-2 2.761×10-1 2.497×10-2

Hg 4.210×10-3 3.39×10-3 4.93×10-3 3.11×10-3

NH3 16.5 15.3 19.5 11.8

According to the concentrations, the average individual risk of Cd and Cr6+, Pb, Hg, NH3 and the total risk of carcinogenic and non-carci-nogenic pollutants (RTotal) from solid waste were calculated using a human health risk assessment model (Equations 1-3) and the relati- ve parameters after they infiltrated into groundwater (Table 4).

Figure 4 and Table 4 show that the human health risks of cadmium in solid waste per year before and


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Table 4. Comparison of total average individual risk of carcinogenic and non-carcinogenic pollutants to human health per year before and after EM treatments

July 2011 August 2011Carcinogenic/non-carcinogenic pollutants

Before treatment

After treatment

% change

Before treatment

After treatment

% change

Cd 5.42175×10-6 4.60040×10-6 15.14 7.58439×10-6 3.03972×10-6 59.92Cr6+ 2.96023×10-4 4.66803×10-5 84.23 2.97284×10-4 3.38309×10-5 88.62Total carcinogenic pollutant 3.01400×10-4 5.12800×10-5 82.99 3. 04900×10-4 3.68700×10-5 87.91Pb 8.94359×10-7 8.20402×10-8 90.83 9.03522×10-7 8.17130×10-8 90.96Hg 3.00032×10-7 2.41594×10-7 19.48 3.51344×10-7 2.21639×10-7 36.92NH3 1.12478×10-10 1.04298×10-10 7.27 1.32929×10-10 8.04391×10-11 39.49

Total non-carcinogenic pollutant 1.19500×10-6 3.23700×10-7 72.91 1.25500×10-6 3.03400×10-7 75.82Total treatment 3.02639×10-4 5.16044×10-5 82.95 3.06124×10-4 3.71740×10-5 87.86

Figure 4. Average individual risk (Rtotal) of the carcinogenic pollutants Cd and Cr6+ and non- carcinogenic pollutants Pb, Hg and NH3 to human health per year: A and C: July 2011, B and D: August 2011.


5226 Int J Clin Exp Med 2016;9(2):5218-5227

by plants and enter the food chain [27], becom-ing a health thread for the consumers [28, 29]. There are numerous published reports about microorganisms as biosorbents for remediation of heavy metal polluted soils [30, 31]. The prin-ciple mechanism is that microorganisms uptake the heavy metals and integrate them into their cell walls, rendering them immobilized and thus water insoluble, and not available for grow-ing crops or lavage [32]. The uptake of heavy metals by biomass can in some cases reach 50% of the biomass dry weight [31], which can explain the excellent decrease to human health risk after EM treatments.

Conclusion

The assessment of solid waste shows that EM treatment reduces the risk to human health of carcinogenic and non-carcinogenic pollutants in landfill leachate. Clearly, EM treatment sh- ould be used for the stabilization and degrada-tion of toxic components in leachate, and will be beneficial for the recovery of the ecological function of leachate polluted water and soil. The results of this research will be useful for the ecological restoration and pollution control of an area surrounding an enclosed landfill site and the human health risk assessment method described can be used for risk evaluation of carcinogenic and non-carcinogenic chemicals in leachate.

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Acknowledgements

Research on the environmen-tal behavior and resource of the living landfill in Harbin (20- 06G0673-00).

Disclosure of conflict of inter-est

None.

Address correspondence to: Hu- iling Liu, School of Municipal and Environmental Engineering, Har- bin Institute of Technology, No. 73 Huanghe Road, Harbin 150- 090, China. Tel: 0451-51019150; Fax: 021-51561341; E-mail: Liu- [email protected]

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