Elsevier

Waste Management

Volume 31, Issue 8, August 2011, Pages 1827-1832
Waste Management

A novel technique of semi-aerobic aged refuse biofilter for leachate treatment

https://doi.org/10.1016/j.wasman.2011.03.016Get rights and content

Abstract

We developed a semi-aerobic aged refuse biofilter (SAARB) for leachate treatment and examined its advantages and disadvantages compared to previous aged refuse biofilters (ARBs). To assess its treatment capability, decontamination mechanisms and optimal performance parameters, a single-period experiment and L9(34) orthogonal array design experiments were conducted on artificial leachate. The SAARB markedly enhanced the treatment capability and removal efficiency of organic matter and nitrogen pollutants due to the alternating aerobic–anoxic–anaerobic zones in situ. The reduction in chemical oxygen demand (COD), ammonia nitrogen (NH4+N) and total nitrogen (TN) exceeded 98%, 94%, and 80%, respectively. After the leachate was distributed onto the SAARB surface, the effluent velocity decreased as a logarithmic function, and there was a concomitant reduction in leachate effluent volume. Based on the capacity for removal of COD, NH4+N, and TN, the effective height of aged refuse in a SAARB was enough to be 900 mm. An excellent treatment efficiency could be achieved at 20–35 °C, with a leachate distribution time of 1 h once every period of 2–3 days, hydraulic loading of 11–30 L/(m3 day), and COD loading of 550–1200 g/(m3 day). This new SAARB system demonstrates superior efficacy for biofilter compared to other ARB systems, especially for nitrogen removal from leachate.

Introduction

Leachate from landfills is one of the most damaging sources of pollution on the surrounding environment (Ritzkowski et al., 2006, Bilgili et al., 2007), due to its complex mixture of pollutants, high chemical oxygen demand (COD), and high ammonia nitrogen (NH4+N) and etc. Leachate emanating from landfills is significant risk to soil, water and air quality (Prantl et al., 2006). Currently, many treatment methods for leachate decontamination, including biological methods, physical and chemical methods, land treatments, and various combinations thereof have been used. When treating young leachate, biological techniques are reasonable effective in reducing COD, NH4+N and heavy metals. When treating stabilized (less biodegradable) leachate, physico–chemical treatments have been found to be an effective refining step following biologically treatment remove refractory organic substances. Integrated chemical–physical–biological processes (in whatever order) ameliorate the limitations of individual processes and result in a higher efficacy of overall treatment (Renou et al., 2008). However, there are still many deficiencies to those methods, including high initial construction costs, operating costs, the large surface areas required, and high energy consumption. These and other constants have made the treatment of leachate a difficult challenge throughout world.

It is well known that aged refuse has both a large specific area and high porosity, and contains a large number of predominant bacteria that have acclimated to a high concentration of pollutants for years (Zhao et al., 2006, Shi et al., 2007). Therefore, the use of aged refuse to treat leachate is one promising alternative. Biofilters are a low-cost leachate treatment technique (Jokela et al., 2002). So recent studies have developed and assessed aged refuse biofilters (ARBs). He et al. (2006) and Long et al. (2008a) combined an ARB with a bioreactor landfill to treat leachate. This system removed organic matter effectively, but ammonia nitrogen decreased only slightly because of the anaerobic conditions within the sealed ARB. In order to deal with this problem, He et al. (2007) devised a tower aged refuse biofilter (TARB) with three airways to improve the removal rate of pollutants, especially NH4+N, and achieved pollutant removal rates ranging from 88.8% to 98.3%. The removal rate of total nitrogen (TN), however, remained low (21.5–65.2%). Later studies (Tao et al., 2009, Li et al., 2009) combined two or three aged refuse biofilters in series to form a multistage aged refuse biofilter (MARB) that could treat leachate more effectively than the TARB. However, the TN removal efficiency of the TARB still did not reach the requirements of environmental protection due to the absence of air circulation. In addition to the shortcomings of the TARB, a large surface area also restricted the application of MARB. Turgut et al. (1998) installed an air pump at the bottom of the reactor to form aerobic, anaerobic, and anoxic zones from the bottom to the top, and achieved 95% nitrogen conversion but with higher energy consumption.

Table 1 presents a comparison of these techniques. Clearly, alternative treatments must be developed.

Building on these technologies, we devised a semi-aerobic aged refuse biofilter (SAARB) and tested its efficiency. The SAARB is a novel leachate treatment technique, in which the diameter of the leachate collection pipe and airway pipe are enlarged and both ends are connected to air. The difference in temperature between the inside and outside of the SAARB drives air into the biofilter, expanding the aerobic zone, and leading to near complete degradation of organic matter, nitrogen pollutants, and others. As a result, the removal efficiency and treatment capacity were enhanced greatly. The operation parameters and treatment mechanisms of SAARB were explored using both a single-period experiment and an orthogonal array design to optimize multiple parameters. The results clearly demonstrated that the SAARB not only overcame many of the disadvantages of MARB and TARB, but also provided a more effective and economical technique for treating leachate.

Section snippets

The SAARB construction

The laboratory scale SAARB was made of a PVC column with an inner diameter of 300 mm and a height of 1100 mm (Fig. 1). At the bottom, one leachate collection pipe and one horizontal airway were fitted, both with a diameter of 25 mm. The other airway, with an open ratio of 12.5%, was inserted vertically down through the center of the SAARB where it connected to the bottom airway. This central airway was 15 mm in diameter with 5 mm perforations spaced at 100 mm. Therefore the air could move into the

The orthogonal experiment

The results of orthogonal array design experiments (Table 4) indicated that the optimal operational parameters of SAARB were “A2B3C2D2”. The most effective treatment was achieved at 30 °C, a leachate distribution frequency of once every 3 days, a hydraulic loading of 8L/(m3 day), and a COD of 40,000 mg/L (viz. 320 g COD/(m3 day)). The most important influences on COD, TN and NH4+N removal rates were the hydraulic loading, leachate distribution frequency and COD respectively.

The effluent velocity and cumulative volume

Fig. 2 clearly shows that

SAARB treatment mechanism

Generally, the process of biological degradation usually generates a significant amount of heat, leading to thermal gradients between the inside and outside of the SAARB systems. It caused natural motive power to drive air into the SAARB from the leachate collection pipe and airway pipe. Dong et al. (2005) and Shao et al. (2008), reported that the oxygen content in a simulated semi-aerobic bioreactor decreased from the top layer (12.2%), through the middle layer (4.2%), to reach a minimum in

Conclusions

The SAARB takes full advantage of the semi-aerobic construction to enhance natural aeration modes that form alternating aerobic–anoxic–anaerobic layers within the SAARB. This made it possible for the SAARB to simultaneously remove nitrogen and organic carbon. This SAARB system was particularly effective in reducing the total nitrogen.

These results suggested that the effective height of aged refuse could be as little as 900 mm with excellent treatment efficiency at 20–35 °C, a leachate

Acknowledgments

This work was supported by the Fundamental Research Funds for the Central Universities of China (No. 2010XS36& No.SWJTU09CX059).

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