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Chapter Five. Pollution Mechanism of Contaminated Construction and Demolition Waste
Chapter Six
Migration Patterns of Pollutants in Construction & Demolition Waste
Abstract
Simulated landfill columns with heavy metal contaminated construction and demolition under different acid rain conditions have been established. Hydration products in cement such as silicate, aluminate, calcium hydroxide, etc. may release into the leachate with rainfall, which ultimately leads to the increase of pH to 11–12. Leaching of inorganic matter during landfilling causes a higher total dissolved solid and electrical conductivity compared with those of municipal and industrial wastewater. On the other hand, the concentration pattern and cumulative release of Cu, Cr, and Cd is arranged in the order of neutral rain (pH = 4.8) < weak acid rain (pH = 5.8) < strong acid rain (pH = 3.8) condition. Zn poses the highest migration capacity whereas Cd has the lowest. Negative exponential model decay model accords well with cumulative release of heavy metals. Decay rate is slow in simulated enclosed workshops even for volatile pollutants, 70% or more can be remained after 120 days. The similar conditions appear around the reaction pool and leaked pipes of enclosed workshops. Sunlight and temperature are the most important regulators of organic pollutant degradation. Residual rate of fenvalerate in the multisystem of water–demolition waste–soil system is approximately 7% higher than that in water–demolition waste system.
Keywords
Acid rain simulation; Decay; Landfilling; Migration pattern; Organic pollutant
6.1. Acid Neutralizing Capacity and Dissolution of Heavy Metal
The construction and demolition (C&D) waste samples soaked in heavy metal solution were dried at 100°C and grinded by electromagnetic pulverizer. The ground samples was sieved by 150 meshes and dried at 100°C. Sample (4 g) was taken for the leaching experiment with HNO3 as the extraction solvent. Under the condition of 1:10 solid to liquid ratio, the sample was extracted for 24 h on a shaker with 110 ± 10 rpm. The extraction solution was centrifuged with 4000 rpm for 20 min, and then filtered with 0.22 μm membrane. pH of the extraction solution was adjusted to 2.0 before measuring concentration of Zn, Cu, Pb, Cr, and Cd.
6.1.1. Acid Neutralizing Capacity
pH is one of the most important factors influencing the leaching of heavy metal. It could test the buffering capacity of C&D waste as well as stabilization ability in acid solution by measuring acid neutralizing capacity (ANC). Many minerals in the sample will dissolve during acid neutralization reaction. Therefore ANC is related to dissolution of CaCO3, C–S–H, and SiO2 gel.
Fig. 6.1 is the ANC capacity curve of C&D waste. Y-axis is ANC with unit acid equivalent, meq/kg. Initial pH of ordinary C&D waste was high and up to 11.02. With the addition of acid, pH dropped dramatically. The linear regression equation of ANC and pH was determined to be y = −1.687x + 10.316, with R2 = 0.9631. At confidence level of α = 0.05, the critical value of R was 0.754. There was close correlation between x and y, the fitting equation was credible.
The pH of heavy metal contaminated C&D waste sample was lower than ordinary C&D waste due to the pretreatment. The slope value of heavy metal contaminated C&D waste was lower than the ordinary sample. With the addition of nitric acid, the decreasing rate was less than the ordinary sample. The linear regression equation of ANC and pH was determined to be y = −2.660x + 9.162, with R2 = 0.9237. At confidence level of α = 0.05, the critical value of R was 0.878. There was close correlation between x and y, the fitting equation was credible.
6.1.2. Dissolution Ability of Heavy Metals
Heavy metal dissolution ability in C&D waste at different pH is shown in Fig. 6.2, which was largely influenced by the acid dose. When ANC < 2 and dissolution pH > 7, Zn, Cu, Pb, Cr, and Cd were not detected in the solutions, and when ANC < 2 and dissolution pH < 6, Zn, Cu, Pb, Cr, and Cd concentrations in the solutions increased with the decrease of pH.
Heavy metal dissolution ability of contaminated C&D waste at different pH is shown in Fig. 6.3, which was largely influenced by the acid dose. When ANC < 2 and dissolution pH > 7, Zn, Cu, Pb, Cr, and Cd concentrations in solutions were very low. When 1 ≤ ANC ≤ 4 and dissolution pH < 6, Zn, Cu, Pb, Cr, and Cd concentrations in solutions increased with the decrease of pH and stopped rising with ANC > 4.
6.2. Migration of Heavy Metals Under Acid Rain
Cylinder made of plexiglass was used to simulate the C&D waste landfilling process. The diagram of setup is shown in Fig. 6.4, with 1.6 m in height, 1.6 m in diameter, 2 m in thickness, and rainfall area of 0.028 m2. Landfilling quantity of each cylinder was 46.1 kg.
Figure 6.2 Heavy metal dissolution ability of ordinary construction and demolition waste. (A) Acid neutralizing capacity (ANC) and heavy metal dissolution curve and (B) pH and heavy metal dissolution curve.
pH of rainfall at 74 monitoring station was found to be among 4.0–7.5. During 1993–2004, average pH of rainfall in East China was 4.96. At the same time, average pH of rainfall around China was 5.39. The anion in the rainfall was mainly 
and 
. Criteria of acid rain intensity classified by EPA of China are listed in Table 6.1.
and . Criteria of acid rain intensity classified by EPA of China are listed in Table 6.1.
Migration of heavy metal in contaminated C&D waste under three kinds of acid rain (strong acid rain, neutral rain, and weak acid rain) conditions is introduced. Simulated rain pH of 5.8, 4.8, and 3.2 was made with H2SO4 and HNO3.
Data of rainfall was cited from Chinese National Statistics Yearbook (2003–12). At the prophase of the landfilling (the first 50 days from middle May to the end of June), rainfall was applied the highest amount of Shanghai monthly rainfall from 2003 to 2012 with every 2 days. At the middle phase of landfilling, rainfall amount was 95% confidence interval upper limit value of Shanghai monthly rainfall amount from 2003 to 2012. From 51st to 82nd day, rainfall was every 3 days one time. From 83rd to 114th day, rainfall was 6 times every month as every 5 days one time. From 115th to 206th day, rainfall was 4 times every month as every 7 days one time.
Every acid condition was adapted to one landfill setup. The experimental condition is given in Table 6.2. For the first period of landfilling, leachate produced at 28th day. Later leachate came out when simulated rainfall was conducted. Leachate amount, pH, electrical conductivity (EC), total dissolved solid (TDS), concentration of heavy metals (Zn, Cu, Pb, Cr, Cd), and calcium were measured.
6.2.1. Leachate Amount Generated in Landfilling
After simulated rainfall was spilled into landfill body, C&D waste absorbed rain and reached saturated state, then leachate came out from the setup. At the 28th day, leachate began to come out from the landfill body. The relationship of leachate amount and simulated rainfall is shown in Fig. 6.5.
According to the figure above, it was shown that leachate came out at 28th day. From 28th day and 36th day, the variation tendency of rainfall amount and leachate amount differed due to the absorbing of C&D waste. Later, the difference between rainfall amount and leachate amount got smaller. After 50–80 days, leachate amount of the three landfill setup varied. Leachate amount under neutral acid (pH = 5.8) was less than that under weak acid (pH = 4.8). Under strong acid rain, powder was corroded inside C&D waste and porosity formed, leading to the less rainfall absorbed. The intensity of corrosion decreased with the increase of pH of rainfall, which led to the decrease of leachate amount. At late stage of 84–149 days, leachate amount and rainfall amount was equal under neutral condition and the water stored in former period was released.
6.2.2. Variation of pH During Landfill Process
A large amount of alkaline matters exist in concrete. Hydration products in cement such as silicate, aluminate, calcium hydroxide, etc. released into the leachate with rainfall, which ultimately led to the increase of pH. pH of leachate was about 11–12, which was nearly the same under three kinds of rainfall conditions. The variation of pH with time is shown in Fig. 6.6. With increase of landfilling time, pH showed a cyclic variation which decreased during the early period and then increased. pH of leachate flowed out during later period was lower. Then pH under these three conditions slowly increased to 11.55, 11.59, and 11.49, respectively.
According to Environmental Quality Standard for Surface Water (GB3838-2002), pH of level I–V water is 6–9. Based on Discharge Standard of Pollutants for Municipal Wastewater (GB18918-2002) and Integrated Wastewater Discharge Standard (GB8978-1996), the demand for the discharged wastewater is 6–9. C&D waste leachate should be neutralized before being discharged.
6.2.3. Electrical Conductivity and Total Dissolved Solid in Leachate
Variation of EC and TDS is shown in Fig. 6.7. EC of C&D waste leachate under neutral acid (pH = 5.8) was lower than that under weak acid (pH = 4.8), while EC of C&D waste leachate under weak acid (pH = 4.8) was lower than that under strong acid (pH = 3.2). There was no significant distinctiveness among the pattern of the three kinds of leachate. The initial leachate EC under neutral acid (pH = 5.8), weak acid (pH = 4.8), and strong acid (pH = 3.2) was 34,300 μs/cm, 34,700 μs/cm, and 39,100 μs/cm, respectively. EC dropped gradually with time in later landfilling phase. EC at 41st day was much lower than the initial leachate EC.
Figure 6.7 Electrical conductivity (EC) and total dissolved solid (TDS) of heavy metals contaminated construction and demolition waste leachate. (A) EC and (B) TDS.
Variation of TDS in the leachate showed similar trend to the variation of EC. TDS of C&D waste leachate under neutral acid (pH = 5.8) was lower than that under weak acid (pH = 4.8), while TDS of C&D waste leachate of weak acid (pH = 4.8) was lower than that under strong acid (pH = 3.2). The initial TDS under the three conditions was 28,084 mg/L, 29,084 mg/L, and 322,236 mg/L, respectively, and also dropped gradually then. Compared to the initial leachate TDS, the TDS of leachate at 40th day decreased one percent.
Table 6.3
Linear Regression Between Total Dissolved Solid (TDS) and Electrical Conductivity (EC) of Heavy Metal Contaminated C&D Waste Leachate
| Rainfall Condition | Regression Equation | R2 |
| pH = 5.8 | TDS = 0.853 EC | 0.9817 |
| pH = 4.8 | TDS = 0.859 EC | 0.9819 |
| pH = 3.2 | TDS = 0.870 EC | 0.9798 |
| Total | TDS = 0.861 EC | 0.9809 |
Good correlation between TDS and EC existed. Liner regression between TDS and EC of 28 leachate samples are shown in Table 6.3. The ratio of TDS and EC increased with the decrease of pH, which indicated that more inorganic matters were released with the decrease of pH.
TDS and EC ratio of municipal wastewater was 0.55, while that of natural water and city water was 0.54 and 0.60, respectively. Linear regression equation between TDS and EC of heavy metal C&D waste leachate was TDS = 0.861 EC (R2 = 0.9809). C&D waste was mainly composed of inorganic matter. Leaching of inorganic matter during landfilling would cause higher TDS and EC than those of municipal wastewater and industrial wastewater. Treatment of leachate should focus on the removal of inorganic matters.
6.2.4. Migration of Heavy Metal and Calcium
Heavy metals and a large amount of calcium in C&D waste migrated from landfill body into water. Variation of Zn, Cu, Pb, Cr, Cd, and Ca concentration of C&D waste leachate is shown in Figs. 6.8–6.12 and 6.14A. Cumulative release of Zn, Cu, Pb, Cr, Cd, and Ca is shown in Figs. 6.8–6.12 and 6.14B.
With the increase of landfill time, concentration of Zn and Cr fluctuated, while that of other heavy metals remained relatively stable. The average Zn concentration was 90–2000 μg/L and reached its maximum value at 50–60 day. Cu concentration of initial leachate under three conditions was 1828.6 μg/L, 1776.1 μg/L, and 2252.4 μg/L, respectively. For Cr, the concentration of initial leachate was 39.1 μg/L, 39.8 μg/L, and 40.5 μg/L, respectively. During the early period of the landfilling course, Cr concentration rose to 500 μg/L (after 55–58 days) with minor fluctuation, experienced a dramatic dropping and then began to rise. Almost the concentration of these heavy metals in all initial leachate exceeded the water limit value level III (Environmental Quality Standard for Surface Water). There was no regulation of Cr in this criterion. However, Cr concentration in all leachate met the demand of Integrated Wastewater Discharge Standards (GB8978-1996). Cd concentration fluctuated within 0–5 μg/L. After 61st day, Cd concentration in leachate decreased below the detection limit.
Figure 6.8 Migration of Zn during construction and demolition waste landfilling. (A) Zn concentration in leachate and (B) cumulative release of Zn.
Figure 6.9 Migration of Cu during construction and demolition waste landfilling. (A) Cu concentration in leachate and (B) cumulative release of Cu.
Cumulative release of Zn under three conditions was arranged in the order of strong acid rain < neutral rain < weak acid rain. For Cu, it was weak acid rain < neutral rain < strong acid rain condition. The pattern is different for Cr and Cd, of which were both neutral rain < weak acid rain < strong acid rain condition. The amount of Cd migrated from C&D waste to leachate was lower than other heavy metals, indicating its poorest migration capacity in cement.
When the monitoring is over, the proportion of the average accumulated release amount in the total amount of the C&D waste landfilling column is demonstrated in Fig. 6.13. The relative release potential is ordered as Zn > Cr > Cu > Pb > Cd.
Variation of Ca concentration in leachate was similar and decreased with time under the three conditions. In waste cement, calcium carbonate was generated with carbonation and controlled the dissolution of Ca. A large amount of Ca was detected in the leachate. Under the condition of pH = 3.2, for example, Ca concentration gradually decreased from 7372 mg/L to 226 mg/L. The cumulative release of Ca was arranged in the order of neutral rain < weak acid rain < strong acid rain condition before 110 days' landfilling, while it changed to weak acid rain < neutral rain < strong acid rain condition after 110 days.
Figure 6.11 Migration of Cr during construction and demolition waste landfilling. (A) Cr concentration in leachate and (B) cumulative release of Cr.
First order reaction equation, Elovich equation and negative exponential decay equation were used to analyze the regression between cumulative release of heavy metals (y, mg) and time (x, d). These equations are listed below in order.
Figure 6.12 Migration of Cd during construction and demolition waste landfilling. (A) Cd concentration in leachate and (B) cumulative release of Cd.
y = A(1 − e−bx)
y = y0 + A × lnx
y = y0 + Ae−x/t
Results are listed in Table 6.4. For Zn, R2 of first order reaction model was less than 0.9. R2 of Elovich model and negative exponential model decay model was higher 0.9. For Cu, Pb, and Cr, R2 of all the three models were higher than 0.9. For Cd, first order reaction model failed to fit the migration pattern while R2 of Elovich model was less than 0.8. For Ca, R2 of Elovich model and first order reaction model was 0.8–0.9 and R2 of negative exponential mode was higher than 0.9. Results showed that negative exponential model decay model accorded well with the cumulative release pattern of all the heavy metals and calcium.
6.3. Migration and Transfer Patterns of Organic Pollutants Under Various Conditions
6.3.1. Effect of Sunlight, Ventilation, Temperature, and Moisture
Concentration and release potential of pesticides and other nonpersistent organic pollutants varied widely with external environmental conditions. Different climatic and environmental factors had been controlled and regulated to investigate the degradation of pyrethroid and other pesticide on surface of C&D waste. Due to the difficulty in the in situ identification of organic pollutants, a system of quick determination of the possible pollution areas with high potential environmental risks should be established.
Persistent organic pollutants usually have long decay time and may be difficult to degrade in the soil or sediment even for years. DDT, a typical representative of high durability, high pollution, high environmental risk pesticide, was already prohibited in the 1980s. As a result, the solid waste contaminated by DDT gradually deposited in the part of the river sediment and soil after being prohibited. The concentration DDT in C&D waste was very small currently. Therefore pyrethroids were selected as the subject due to its large production and wide usage.
Figure 6.14 Migration of Ca during construction and demolition waste landfilling. (A) Ca concentration in leachate and (B) cumulative release of Ca.
Simulated extreme environments and condition of abandoned industrial C&D waste within the workshops were carried out, pyrethroid pesticide-contaminated were placed in a cool, dry, and enclosed place with good ventilation, the pesticide residues were detected 120 days later, and the residual rate is shown in Table 6.5.
Table 6.4
Regression Between Cumulative Release of Metals and Time
| Landfill Condition | First Order Reaction Model | Elovich Model | Negative Exponential Decay Model | |||
| Regression Equation | R2 | Regression Equation | R2 | Regression Equation | R2 | |
| Zn | ||||||
| pH = 5.8 | y = 23.56(1 − e−0.005x) | 0.886 | y = −21.61 + 6.89lnx | 0.964 | y = 12.11 − 24.01e−x/38.419 | 0.987 |
| pH = 4.8 | y = 23.98(1 − e−0.006x) | 0.875 | y = −23.12 + 7.38lnx | 0.958 | y = 12.83 − 26.68e−x/36.434 | 0.988 |
| pH = 3.2 | y = 23.16(1 − e−0.005x) | 0.886 | y = −19.61 + 6.19lnx | 0.966 | y = 10.95 − 20.65e−x/51.487 | 0.984 |
| Cu | ||||||
| pH = 5.8 | y = 20.77(1 − e−0.005x) | 0.989 | y = −15.04 + 5.02lnx | 0.989 | y = 14.18 − 15.68e−x/105.32 | 0.987 |
| pH = 4.8 | y = 46.81(1 − e−0.002x) | 0.987 | y = −18.02 + 5.79lnx | 0.974 | y = 20.02 − 21.48e−x/158.70 | 0.988 |
| pH = 3.2 | y = 57.38(1 − e−0.002x) | 0.990 | y = −22.19 + 7.13lnx | 0.978 | y = 24.75 − 26.52e−x/159.54 | 0.984 |
| Pb | ||||||
| pH = 5.8 | y = 58.12(1 − e−0.004x) | 0.977 | y = −41.26 + 13.5lnx | 0.997 | y = 32.51 − 39.73e−x/80.46 | 0.997 |
| pH = 4.8 | y = 48.68(1 − e−0.003x) | 0.979 | y = −28.92 + 9.34lnx | 0.994 | y = 23.72 − 28.16e−x/92.48 | 0.997 |
| pH = 3.2 | y = 39.45(1 − e−0.004x) | 0.976 | y = −27.91 + 9.13lnx | 0.996 | y = 22.08 − 26.91e−x/80.97 | 0.996 |
| Table Continued | ||||||
| Landfill Condition | First Order Reaction Model | Elovich Model | Negative Exponential Decay Model | |||
| Regression Equation | R2 | Regression Equation | R2 | Regression Equation | R2 | |
| Cr | ||||||
| pH = 5.8 | y = 11.30(1 − e−0.005x) | 0.909 | y = −9.47 + 3.03lnx | 0.977 | y = 5.56 − 9.85e−x/43.35 | 0.985 |
| pH = 4.8 | y = 12.07(1 − e−0.004x) | 0.907 | y = −9.55 + 3.04lnx | 0.976 | y = 5.55 − 9.74e−x/44.58 | 0.983 |
| pH = 3.2 | y = 62.82(1 − e−0.0008x) | 0.951 | y = −12.51 + 3.87lnx | 0.991 | y = 8.68 − 26.91e−x/81.45 | 0.987 |
| Cd | ||||||
| pH = 5.8 | – | – | y = 15.63 + 9.47lnx | 0.695 | y = 59.26 − 143.95e−x/13.77 | 0.967 |
| pH = 4.8 | – | – | y = 10.30 + 10.87lnx | 0.717 | y = 60.64 − 122.51e−x/15.80 | 0.955 |
| pH = 3.2 | – | – | y = 19.27 + 12.57lnx | 0.580 | y = 76.12 − 844.00e−x/8.28 | 0.884 |
| Ca | ||||||
| pH = 5.8 | y = 39.67(1 − e−0.02x) | 0.872 | y = −30.37 + 13.99lnx | 0.857 | y = 34.87 − 93.17e−x/20.53 | 0.938 |
| pH = 4.8 | y = 38.89(1 − e−0.02x) | 0.854 | y = −27.73 + 13.46lnx | 0.822 | y = 34.40 − 128.9e−x/16.66 | 0.955 |
| pH = 3.2 | y = 39.86(1 − e−0.02x) | 0.850 | y = 26.96 + 13.55lnx | 0.811 | y = 35.49 − 144.1e−x/15.80 | 0.957 |
Table 6.5
Residual Rate of Pyrethroid Pesticides on C&D Waste After 120 days (%)
| Residual Rate (%) | |||||||||||||
| 73.3 | 84.4 | 42.9 | 100.6 | 82.3 | 79.5 | 70.6 | 74.5 | 49.1 | 56.1 | 78.3 | 77.3 | 79.7 | 92.1 |
Based on the results listed above, the decay rate was slow in simulated enclosed workshops even for volatile pesticides. The residual rate could be up to 70% or more for most waste samples, and some kinds of pesticide hardly degraded. The similar conditions appeared around the reaction pool, leaked pipes of enclosed manufacturing workshops and should be the contaminated regions with high potential risks.
To further explore effects on pesticide degradation, other climatic conditions such as ventilation, sunshine were separately regulated. Contaminated C&D waste was placed under different ventilation and sunshine simulated environment for 48 h, and the pesticide residue was detected once every 6 h. The results are shown in Fig. 6.15.
As shown in Fig. 6.15, the decay rate continued to slow down under certain conditions. As the ventilation conditions got better, pesticide decay rate increased first and then decreased. In cool, dry and enclosed environments, decay rate of volatile pesticides was still slow, which matched the results of residual rate under simulated environments. Sunlight and temperature were the most important regulators that meant the potential environmental risks of pyrethroid contaminated C&D waste would be largely reduced under sun or high temperature.
6.3.2. Migration of Pesticides in Simulated Washing Procedure
Decay time of volatile pesticides under the cool environment with low ventilation is long and potential environmental risk exists. For this kind of C&D waste, the possible migration and wash off with water should be investigated to get a further knowledge of its contamination and transformation pathways. The pyrethroid pesticides with low water solubility were used as target pollutants. Simulated seepage of water was carried out by adding water from the top. The flow was set as medium-intensity. The sampling outlet was set on the bottom. The water was continuously added for 24 h and added for another 24 h after a day's interval. The leachate was collected and analyzed in frequency. According to the results, four pollutants with typical patterns were selected (A1 bifenthrin, A2 fenpropathrin, A3 beta-cyfluthrin, and A4 cypermethrin). The relationship between concentration in water (a) and in C&D waste (b) and the duration is demonstrated in Fig. 6.16.
The elution pattern figure showed that in early time period, large amounts of pesticides could be taken away with water. With the increase of injection time, the amount of pesticide taken away in certain time period rapidly reduced, and then gradually stabilized. The removal rate of pesticide with water tended to be constant.
When the flow stopped, the holding capacity of the surface water of C&D waste had some influence on the migration of pesticides, which is reflected in the curve projection in Fig. 6.16A. In the 24 h without injection of water, the pesticides on the surface of waste continuously dissolved in the residual water while the holding capacity of water of C&D waste prevented the water from dropping down. When the injection of water began, this portion of pesticide was washed off through water, which caused the immediate increase of pesticide amount in the wash-off water.
Different types of pyrethroid pesticide varied widely in release curve that may be due to the characteristic (e.g., solubility and viscosity) of pesticide itself. In the environment of the real industrial workshops, C&D waste is often mixed with soil, and make up a multisystem of water–C&D waste–soil. To further study the potential migration risk in a complex system, a new elution column based on this system was established. Fenvalerate was chosen as the contaminant and the device is shown in Fig. 6.17. The device is devised as enclosed except for the inlet and outlet to minimize the volatilization of organic pollutants.
Figure 6.16 Elution pattern of pyrethroids in construction and demolition waste by simulated seepage. (A) Elution rate curve and (B) pesticide residues–elution time curve.
The wash-off water of 5–10 min, 15–20 min and 30–35 min was collected and analyzed using GC–MS. Results showed that the concentration of fenvalerate in system 2 was lower than that in system 1, which is listed in Table 6.6. The procedures were repeatedly conducted and all the C&D waste were collected and extracted. The extraction liquid was merged with the elution (wash-off water) and pretreated for GC–MS analysis. Results showed that the total amount of fenvalerate in system 2 was about 7% less than that in system 1.
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