Bioremediation of Polluted Sediments of Urban River and its Affections to the Overlying Water Bioremediation

By MingYu Li¹ *, Xiaowei Liu¹, DanPing Xie², KaiMing Li²
July 2011

  1. Department of Environmental Engineering, Jinan University, Guangzhou, China   *Corresponding Author
  2. South China Institute of Environmental Science .MEP, Guangzhou, China
Abstract
The release of pollutants from the river sediment causes serious secondary pollution to the overlying water. Aims to find an effective way to control the release of pollutants from sediment, we studied on the bioremediation of contaminated sediment and its effects to the bioremediation of overlying water through a series of well controlled experiment that deal with the joint implementation method of aeration - bioaugmentation by using a continuous flow model river. The results showed that, the joint implementation method could achieve a good effect to the sediment bioremediation. This method could effectively improve the activity of the biodegradation of sediment (G value) from 0.20∼0.25kg/kg·h to 0.42∼0.47kg/kg·h and reduce the release amount of nitrogen and phosphorus pollutants from sediment. Sediment G value (y, kg / (kg · h)) emerged negatively correlated relationship (y = 0.5124x1-0.1394 (R² = 0.9222), y = 0.17772x2-0.4781 (R² = 0.8701)) with the amount of emission of nitrogen (x1, mg / (m² · h)) and phosphorus pollutants (x2, mg / (m² · h)). Those both had a good repairing effect on bioremediation of polluted water by using aeration or adding indigenous microbial preparation method separately, but the bioremediation of river sediment had a serious impact on the efficacy of water bioremediation. After the sediment bioremediation, bioremediation of water bodies could get a more significant treatment effect. The maximum removal rates of COD and ammonia nitrogen increased from 65.0% and 16.30% to 72.0% and 41.0% separately, and the water bioremediation cycle shortened from 13d to 6d.

Keywords: Urban river, Contaminated sediments, Release, Water pollution, Bioremediation

Introduction

In the city’s rapid development and industrialization, a large number of wastewater has discharged into the river, and cause the pollution to the overlying water and sediment. Excessive pollutants that deposit in river sediment will be released into the water as a source of secondary pollution (Walker et al., 1999) and it will be a significant impact on the effective management of urban rivers (Morin and Morse, 1999).

Sediment pollution has received increased attention for its widespread and difficult to handle. Effective management of sediment is the key point of the river management project in the pollution control (Hu et al., 2001; Petticrew and Arocena, 2001). The treatment technology of sediment contains physical,chemical and biologic (Perelo, 2010). Gerlinde Wauer found that the addition of chemical additive Depox could effective reduce the release of phosphorus from sediment through the precipitating action (Wauer et al.). Tomaszewski’s study showed that the release of pollutants from sediments could be effectively reduced by covered with active carbon (Tomaszewski et al., 2006). Varjo investigated the effect of three different gypsums to reduce the release of methane and phosphorus. And the result showed the redox potential of sediment had obviously increased, so the release rate of pollutants were decreased (Varjo et al., 2003). In particular, the sediment bioremediation technology has been researched by many scholars and used as engineering applications for its many advantages compared with the physical and chemical remediation (Boopathy, 2000). After the bioremediation of sediment, an expositive action had emerged on the formation of sediment stain resistance system through the research of Vezzulli L (Schratzberger et al., 2003; Vezzulli et al., 2004; Watanabe, 2001).

The objectives of this research were to:

  1. find an effectively bioremediation method for the urban river management under the continuous flow conditions;
  2. investigate the influence of sediment bioremediation to the release of sediment pollutants and bioremediation of upper water.

1 Materials and Methods

1.1 Materials

Samples of sediment and polluted water were collected from the upper reaches of Guliao River (Guangzhou, China).This river section was narrow and seriously contaminated by municipal and industrial wastewaters.

The simulative riverway installation comprised of gathering ground, water distribution area and analog river way. It was built by the brick and covered the bottom by the concrete with the length of 15m, width of 0.70m, total depth of 1.20m and slope of 0.003 each stream channel. The effective volume of each channel was 12.6m³. Each channel was filled with 0.10m of sediment. During the experiment incubation, water flow of each cell of the river was 6.0m³ / d, and the HRT was 2d. As shown in the Figure 1.

Figure 1 · Sketch of Simulated Urban River
Figure 1

1.2 Experimental Methods

Two group experiments were carried out with water continuously flowing into the simulation of river. During the experiment of first group, 30mg/L complex bio-oxidation preparation and 50mg/L indigenous microbial agents were added for sediment repaired. After 2 days continuous treatment to the sediment, the overlying water was governed with aeration and indigenous microbial agents. During the duration of water remediation, the amount of aeration was controlled as follow: 0,1.44 m³ / h, 1.92m³ / h, 2.16m³ / h, 2.7m³ / h, in order to maintain dissolved oxygen as 0 (<0.5mg / L), 0.6 – 2.5 mg / L, 1.5 – 3.5mg / L, 3.0 – 5.0 mg / L, and 4.5 – 6.0 mg / L. Meanwhile the indigenous microbial agent was sprinkled with the dosage of 20mg / L for 5 days. The experiment of second group was identical with the first group except the restoration of sediment. The water samples of inlet and outlet were collected to analyze the water’s CODcr (Lee and Shoda, 2008) NH3-N (Groeneweg et al., 1994), TP (Park and Jung, 2011) PO43- (Rydin et al.); meanwhile the sediment biodegradability (G value) index was also tested. We analyzed the effect of sediment bioremediation, the mechanisms of sediment nitrogen, phosphorus released and the effect of bioremediation of overlying waters that aerated under different conditions after sediment bioremediation.

The sediment biodegradability (G value) was tested with the method as follow: 0.2 g dried sediment was added into the 250 mL flask, then add 100 mL boiling water of Gu Liao Chung that has boiled for 10min, after that, placed in shaker oscillation 6h, and 30min standing. The overlying water samples were taken for the test of COD. Sediment G value is calculated based on COD value of water bodies before and after the oscillation as follows:

Formula

where, G is the sediment biodegradability (kg/(kg·h)), C1 and C2 are the COD value of water before and after test (mg/L), V is the volume of sample (ml), q is the weight of air-dried sediment (g), t is the oscillation time (h).

Figure 2 · Variety of G index in the bioremediation
of sediments under different sediments
treatment conditions
Figure 2

2 Results

2.1 Property changes of sediment during sediment bioremediation process

Bioremediation of sediment could effectively improve the sediment biotope, and formed aerobic environment that had active effect on the evolution of aerobic microbial communities (SHAN et al., 2009). Meanwhile, the microbial activity of sediment was improved, and the degradation of sediment organic matter had strengthened. Variety of G index under different sediment treatment conditions could be seen from Figure 2. After 18d experiment, sediment of the experimental group which had been bioremediation, gradually been restored, and the sediment G value increased gradually. In the aerobic condition of 1.44 ∼ 2.16m³ / h, G value of the sediment increased from 0.20 ∼ 0.25kg/kg · h to 0.42 ∼ 0.47kg/kg · h. While the G value of the experimental group without biological repair of the sediment changed little. Under the aerobic conditions of this experiment, the different amount of aeration had little impact on the change of sediment bio-oxidation rate and G values. So, the sediment could be effective repaired by adding agents for bioremediation of sediment and aerating simultaneously.

Figure 3 · Correlation between G index and the
quantity of nitrogen released during the
bioremediation of sediments
Figure 3

2.2 The impact of sediment bioremediation on nitrogen and phosphorus pollutants release

Figure 4 · Correlation between G index and the
quantity of phosphorus released during the
bioremediation of sediments
Figure 4

Bioaugmentation and water aerating provided adequate oxygen and electron acceptor for sediment, so that the anaerobic or anoxic sediment transformed to aerobic, oxidation reduction potential improved, and the Fe2+ was oxidized to Fe3+ which could combine with phosphate and precipitate in the form of iron phosphate. For this reason, it was conducive to control and reduce the release of phosphate from sediment (Wang et al., 2008). On the other hand, microbial metabolism of sediment also had some influences on the release of nitrogen and phosphate, especially the nitrification of nitrobacteria that acted on ammonia dissolved in the interstitial water was conducive to control and reduce the release of ammonia to the water from sediment (Eggleton and Thomas, 2004). The results of this experiment indicated that, G value was negatively correlated with the nitrogen and phosphate pollutants emission during the duration of sediment repairing. The corresponding relationship between the changes of G value and the amount of nitrogen and phosphate pollutants release were shown in the Figure 3 and Figure 4. The figures showed that, with the bioremediation of sediment and increase of the value of G index, the release of nitrogen and phosphorus pollutants was decreased. The relation of G value (y, kg / (kg · h)) and release of NH3-N (x1, mg / (m² · h)), PO43- (x2, mg / (m² · h)) were as follows: y = 0.5124x1 – 0.1394 (R² = 0.9222), y = 0.17772x2 – 0.4781 (R² = 0.8701).

Figure 5 · Influence of different oxygen aeration
conditions on the removal rate of COD pollutant
in water bioremediation before sediments
remediation
Figure 5

2.3 Influence of the bioremediation of sediment to the aeration - microbial remediation treatment of water bodies

2.3.1 Effect of sediment bioremediation to the removal of CODcr

The influent that composed by domestic sewage and industrial effluent was mainly affected by the rising tide and ebb. So the water quality changes largely, and the concentration of COD was fluctuated between 165.0 ∼ 250.0mg / L. Although the aeration amount had been controlled as 0,1.44 m³ / h, 1.92m³ / h, 2.16m³ / h, 2.7m³ / h, the DO concentrations were respectively changed at 0 (<0.5mg / L), 0.6-2.5 mg / L, 1.5 – 3.5 mg / L, 3.0 – 5.0 mg / L, 4.5 – 6.0 mg / L for the impact of water quality changes.

Figure 6 · Influence of different oxygen aeration
conditions on the removal rate of COD pollutant
in water bioremediationafter sediments
remediation
Figure 6

In the two conditions that repair or without repair of sediment, indigenous microbial agent under different aeration conditions was used to repair the simulated river water. The Figure 5 showed that, under the condition without repair of sediment, the concentration of COD of effluent water was increased. Due to the release of pollutants from untreated contaminated sediment, the water quality had worsened without aeration. By contrast, the concentration of COD of the experimental groups which was aerated by the air decreased significantly. But the removal rate of COD of the simulative river water was much dissimilar under different oxygen supply levels. During the incubation, the aeration rate was separately controlled at 1.44m³/h, 1.92m³/h, 2.16m³/h and 2.7m³/h. Under those conditions, the mean COD of effluents were 70.83mg/L, 61.9mg/L, 61.5mg/L, 73.6mg/L, while the COD of influent water was 140.0∼180.0mg/L. After 20 days experiment, the average removals reached 54.7%, 60.44%, 65.0% and 53.4% separately.

Figure 6 shows that, under different conditions of oxygen supply levels, mean concentration of effluent water were decreased to 105.0mg/L, 60.0mg/L, 50.8 mg/L, 45.2 mg/L and 61.3 mg/L after 18 days bioremediation of sediment that lasted, while the average COD concentration of influent was 161.5mg / L. The average removals were 35.0%, 62.8%, 68.5%, 72.0% and 62.0%.

As seen from the experimental results, the bioremediation of sediment had a greater influence on the restoration of overlying water (Colwell, 2002). After the completion of bioremediation of sediment, operational method combined by aeration and the addition of indigenous aerobic microbial agents achieved a better effect on the COD removal that increased about 10% than that without bioremediation of sediment; When water restoration reached stable, COD was maintained at lower levels, and reduced 15mg / L relatively; Water restoration efficiency increased significantly. The cycle, that the effect of water bioremediation reached stabilized, shortened from 13d to 6d after bioremediation of sediment; after the bioremediation of sediment, maintaining a relatively low amount of oxygen supply level could also achieve a better restoration result.

The method combined by aeration and the addition of indigenous aerobic microbial agents was an effect way for bioremediation of polluted river water. However, the control of amount of aeration had a great effect on the bioremediation of water. In this study, the amount of aeration was controlled at 1.92∼2.16m³/h. Maintaining the DO at 3.0mg / L could achieve better effect of bioremediation of overlying water. However the choice of aeration method was worth studied, because excessive aeration would cause agitation of sediment, and affect the effect of water bioremediation.

Obviously, bioremediation of sediment was more favorable to bioremediation of water. There were three main reasons. Firstly, bioremediation of sediments effectively inhibited the release of pollutants in the sediments to the overlying water that might cause a continuous secondary pollution, meanwhile reduces the degree of water pollution load, and cuts some of the water source, so the effects of water restoration is more significant. Secondly, bioremediation of sediments significantly reduced oxygen demand because of the sediment organic matter and reducing substances consumption. At the same time, the operating factor of dissolved oxygen in the water bioremediation had greatly increased, so that water pollutants was effectively biodegraded (Wang et al., 2008). Thirdly, bioremediation stimulate the formation of aerobic microbial communities in surface sediments, so bio-degradation activity greatly increased and it played a synergistic role in bioremediation of water bodies.

Figure 7 · Influence of sediments bioremediation
on the removal rate of NH3-N pollutant in water
bioremediation under different oxygen aeration
conditions
Figure 7

2.3.2 Influences of sediment bioremediation to the removal effect of ammonia nitrogen

The experiment results showed that (Figure 7), without bioremediation of sediment, the remediation of stimulate river water bodies had limited effect on the removal of ammonia nitrogen. The removal rate of ammonia nitrogen was gradual increased with different oxygen supply level after the operation was stable. At the aerobic condition of 0, 1.44m³/h, 1.92m³/h, 2.16m³/h and 2.7m³/h, the average removal rate of ammonia nitrogen were 8.0%, 13.8%, 15.0%, 16.0% and 8.0%, 20 days later. The experiment results showed that, the removal rate of ammonia nitrogen of different experiment group with different aerobic conditions was increased significantly after the bioremediation of sediment, separately reached 9.9%, 19.0%, 40.0%, 41.0%and 40.6%.

Figure 8 · Influence of sediments bioremediation
on the removal rate of phosphate pollutant in
water bioremediation under different oxygen
aeration conditions
Figure 8

According to the analyzing of the experiment results (Figure 7), although adding indigenous microbial agents could attain the certain result, the joint treatment of bioremediation that aeration of overlying water and adding indigenous microbial agents could achieve a better effect. Meanwhile, sediment bioremediation could not only greatly raised the water bioremediation effect than without sediment biological repair, and make the joint treatment of bioremediation effect more remarkable than a single dosing indigenous microbial agents. This was mainly because after the bioremediation of sediment, sediment transforms from anaerobic state to oxygen state, and the sediment release of ammonia nitrogen to water bodies had been effectively controlled (Fabiano, 1998), so the whole simulation river water repair effect significantly was enhanced. Then, with the improvement of dissolved oxygen levels, abundant of nitrifying bacteria was growing, so it had promoted transformation of the ammonia nitrogen to nitrate, or other forms of nitrogen (G, 1998), and water ammonia nitrogen was reduced greatly.

2.3.3 Effect of sediment bioremediation to the phosphorus removal

Figure 8 showed that, sediment bioremediation under different aeration conditions had little effect on the removal rate of phosphate and phosphorus, this might because the river water phosphate and TP concentrations were high, while the release rate and release quantity of phosphorus were relatively small. Within 2 days water retention time of the simulated river, the release of total phosphorus was lesser than the concentration of influent water. After bioremediation of the aaA sediment, the control of the amount of P that release to the overlying water hadrelatively little influence to the P concentration of overlying water (Gomez et al., 1999).

Different aerobic condition had great influence on the phosphorus removal efficiency during the period of water bioremediation. With the increase of oxygen (0 ∼ 2.16 m³ / h), the removal rate of simulated river water phosphate was gradual enhancement, compared with the treatment group without aeration, the average removal rate of phosphate of the experiment group that using bioremediation processing of aeration - dosing indigenous microbial agents had improved about 25.8% and reached 33.5%; The total phosphorus removal efficiency was also improving along with aeration increases gradually (0 ∼ 1.92 m³ / h), and the largest removal rate reached 20.5%. But with aeration of simulate river further increased, it produced certain disturbance to the sediment, so the treatment effect declined. In this experiment, the best aeration amount for the removal of phosphorus by simulated river water bioremediation was 1.92 m³ / h.

3 Conclusions

The experimental research showed that the effect of sediment remediation only by aeration was not apparent. Sediment G value had little changes. Adopting the joint treatment of aeration and adding indigenous microbial agents could achieve good sediment bioremediation effect. When the aerobic supply levels was more than 1.44 m³ / h (maintain water dissolved oxygen concentration > 1.5 mg/L), and cooperating with adding sediment bioremediation preparations, could achieve good effect of sediment bioremediation. After 18d experiment, sediment G gradually increased, that increased from 0.23 kg / (kg·h) to 0.45kg/(kg·h).

Sediment bioremediation could effectively control and reduce its pollutant release and pollution to overlying water. During the experiment of sediment bioremediation, Sediment G value (y, kg / (kg · h)) emerged negatively correlated relationship (y = 0.5124x1 – 0.1394 (R² = 0.9222), y = 0.17772x2 – 0.4781 (R² = 0.8701)) with the amount of emission of nitrogen (x1, mg / (m² · h)) and phosphorus pollutants (x2, mg / (m² · h)).

After the completion of bioremediation of sediment, operational method combined by aeration and the addition of indigenous aerobic microbial agents could achieve a better effect on the water bioremediation (Fabiano et al., 2003). Controlling the aeration condition to make water dissolved oxygen levels reach 3.0 mg/L (aeration amount 1.92 – 2.16 m³ / h) and above, could achieve good water bioremediation effect, and water COD, ammonia nitrogen and phosphorus removal rate respectively reached 16.30% and 20.5%, 65.0%.

Sediment bioremediation had a large influence on the effects of water bodies bioremediation, and sediment repair could not only reduce the pollutant release to water bodies to produce secondary pollution, but also might strengthen water and sediment bioactivity of biological catabolic synergy (Gadd, 2004; ZHANG et al.). Furthermore it could improve the removal rate of water pollutants, and shortened the water body restoration period. After the sediment bioremediation completed, the bioremediation of water treatment effect was more remarkable, and in the same experiment conditions, the removal rates of COD and ammonia nitrogen increased to 72.0% and 41.0% respectively, meanwhile the bioremediation cycle of water was shortened from 13d to 6d.

Acknowledgement

The present work was financially supported by Projects Under Scientific and Technological Planning of Guangdong Province (No. 2003A3040402)

References

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