Key Takeaways & Executive Findings
- •• • Pressurized nitrogen gas injection after liquid amendments achieved a radius of influence of 5.0 m in low-permeability bedrock fractures, overcoming mass transfer limitations and ensuring uniform distribution of nutrients and bacteria. • • Combined injection of slow-release (emulsified vegetable oil) and soluble (sodium citrate) carbon sources maintained ORP below -100 mV for over one year, creating sustained anaerobic conditions essential for reductive dechlorination. • • The slow-release carbon source (emulsified vegetable oil) reduced injection frequency, lowering operational costs while providing stable electron donors for dechlorinating bacteria. • • The BS-1 culture achieved >95% removal of vinyl chloride, cis-1,2-dichloroethylene, trichloroethylene, and chloroform via anaerobic reductive dechlorination, with groundwater quality occasionally meeting Class IV of GB/T 14848-2017.
Abstract
Chlorinated aliphatic hydrocarbons (CAHs) are prevalent groundwater contaminants at industrial sites in China. This pilot-scale study evaluated in-situ anaerobic bioremediation of CAHs-contaminated groundwater in a low-permeability bedrock fracture zone at depths up to 40 m. A self-developed anaerobic dechlorinating culture (BS-1), containing Dehalococcoides, Desulfitobacterium, and Dehalogenimonas, was injected alongside carbon sources (sodium citrate and emulsified vegetable oil) and nutrients. Pressurized nitrogen gas injection enhanced the distribution of amendments, achieving a radius of influence of 5.0 m. Over 399 days of monitoring, the combined use of slow-release and soluble carbon sources maintained anaerobic conditions (ORP < -100 mV) for over one year, providing sustained electron donors. The emulsified vegetable oil reduced injection frequency and operational costs. The BS-1 culture effectively dechlorinated vinyl chloride, cis-1,2-dichloroethylene, trichloroethylene, and chloroform, achieving removal efficiencies exceeding 95%. At times, groundwater quality met the Class IV standard of GB/T 14848-2017. This study demonstrates a green, economical, and effective solution for CAH-contaminated site remediation, with significant engineering application potential.
1. Introduction
Chlorinated aliphatic hydrocarbons (CAHs) are among the most persistent and toxic groundwater contaminants at industrial sites, posing significant risks to human health and ecosystems. Conventional remediation approaches, such as pump-and-treat or chemical oxidation, often prove inefficient in low-permeability fractured bedrock aquifers due to limited reagent delivery and contaminant mass transfer. These methods also incur high energy and operational costs, making sustainable and cost-effective alternatives imperative.
In-situ anaerobic bioremediation, leveraging organohalide-respiring bacteria, offers a promising solution by degrading CAHs through reductive dechlorination. However, field applications face challenges in delivering bacteria and substrates to deep, low-permeability zones and maintaining favorable geochemical conditions over extended periods. This pilot study addresses these bottlenecks by employing pressurized nitrogen gas injection to enhance amendment distribution and combining slow-release and soluble carbon sources to sustain anaerobic conditions. The results demonstrate a technically viable and economically efficient approach, providing a benchmark for full-scale implementation.
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ZHUANG Jianhong, XING Yuquan, LIU Kun, CHEN Lüjun, CHEN Boyang (2026). Pilot-scale Study on Enhanced In-situ Anaerobic Bioremediation of Chlorinated Hydrocarbon-Contaminated Groundwater in a Low-Permeability Bedrock Fracture Zone. Journal of Environmental Engineering Technology. https://doi.org/10.13205/j.hjgc.202605014
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Frequently Asked Questions
What is the maximum depth and lithology where this bioremediation approach has been validated?
The pilot study was conducted in a low-permeability bedrock fracture zone at depths up to 40 m. The successful injection and distribution of amendments, aided by pressurized nitrogen gas, indicate the method's applicability to similar fractured bedrock aquifers.
How does the pressurized nitrogen gas injection improve amendment distribution in low-permeability media?
Pressurized nitrogen gas injection after liquid amendments creates preferential flow paths and enhances advective transport, effectively increasing the radius of influence to 5.0 m. This overcomes the limited permeability and ensures more uniform distribution of nutrients and bacteria.
What are the long-term maintenance requirements for the slow-release carbon source?
The emulsified vegetable oil serves as a slow-release carbon source, providing a stable supply of electron donors for over one year. This reduces the frequency of carbon source injections, lowering operational costs and minimizing system disturbance.
What are the degradation efficiencies for individual CAHs, and are there any toxic intermediates?
The BS-1 culture achieved >95% removal of vinyl chloride, cis-1,2-dichloroethylene, trichloroethylene, and chloroform. Complete dechlorination to innocuous end products (e.g., ethene) was indicated, with no accumulation of toxic intermediates reported.
How does the cost of this bioremediation approach compare to conventional methods?
The use of slow-release carbon sources and pressurized gas injection reduces injection frequency and operational costs. While specific cost figures are not provided, the approach is described as economically viable and more sustainable than conventional methods, with potential for full-scale application.
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