PRB技术及其在地下水修复中的应用概述

PRB技术是一种将溶解的污染物从污染水体和土壤中去除的钝性处理技术，具有持续原位处理多种污染物、处理效果好、安装施工方便、性价比较高等优点。目前，欧美一些发达国家已对其进行了大量的试验及工程技术研究，并投入商业应用。在我国仍处于试验摸索阶段。

PRB技术的基本原理

PRB技术是在地下安置活性材料墙体以拦截污染羽状体，使污染羽状体通过反应介质后，污染物能转化为环境接受的另一种形式，从而使污染物浓度达到相关水环境质量标准。PRB主要由透水反应介质组成,通常置于地下水污染羽状体的下游，与地下水流相垂直(图A)。 Pollution removal mechanisms include adsorption, oxidation-reduction, and biological degradation, which make the water pollutants removed.

The Structure of PRB and its Installation Method

2.1 The Structure of PRB: According to the structural form, PRBs are divided into two categories: continuous wall-type PRBs (Fig. A), and funnel-leakage well-directing gate-type PRBs (Fig. B).

2.1.1 Continuous Wall-Type PRBs: When the impact range of underground water pollution is relatively small, a permeable reactive barrier can be placed vertically along the migration path of the pollution plume.

2.1.2 Funnel-Leakage Well-Directing Gate-Type PRBs: These consist of funnels with closed plates or mud walls embedded in impermeable layers to guide or collect groundwater flow through active materials for treatment.

2.2 Installation Methods:

Shallow Installation Method: Suitable for depths not exceeding 10 m.

Deep Installation Method: Suitable for depths greater than 10 m.

3 Active Materials Selection and Mechanism

3.1 Active Materials Selection:

Active materials must be suitable for underground environments,

not produce harmful chemical reactions or byproducts during reaction,

and not easily dissolve or consume during reaction.

Materials should also have a suitable particle size to avoid excessive residence time in the material.

Commonly used active materials include zero-valent iron (ZVI), activated carbon (AC),

zeolite (ZL), limestone (LS), ion exchange resins (IERs),

iron oxides and hydroxides,

phosphates,

organic materials such as urban composts,

Organic Matter Removal Mechanisms:

Fe0 → Fe²⁺ + e⁻

RCl + H⁺ + e⁻ → RH + Cl⁻

Fe0 + RCl + H⁺ → RH + Cl⁻+ Fe²⁺+ H₂

In addition to organic matter removal mechanisms,

Zero-valent Iron(PRBS) also removes inorganic ions through oxidation-reduction reactions.

Oxidation Reduction Reactions:

Fe³⁺ -> Fe²‒

CrO₄²‒ -> Cr³‒

4H²O

UO₂⋅SO₄ ⎯→ U(S)

6H₂O

5CH₂O(S)+ NO₃⋅N₀₃⋅NO₃⋅NO₃⋅NO₁

N₀₁ N₀₁ N₀₁ N₀¹

Me²++ HS(aq) -> MeS(s)

2H+(aq)

Microbial Activity in Soil Remediation:

Microorganisms play a role in nitrogen cycling.

They can directly remove nitrate from soil using microbial activity.

Biological Nitrogen Removal Mechanisms:

5CH₂O(S)+ 4NO₃‿⎯→ 2N₂

5HCO₃‿⎯→ CH₄(HC)

Application Examples

In North America and Europe, numerous engineering studies have been conducted on this method; over 120 permeable reactive barriers have been installed.

Two examples will be briefly introduced below.

US Elizabeth Coast Guard Air Station at Elizabeth City Airport has severe chromium VI contamination issues; Cr6+ levels reach up to 14,500 g/kg.

450 tons of shredded iron were used as an active material; constructed with a length of 45 meters deep at 5 meters thick.

Principle components were added as follows:

Zerovalent Iron - 100%

Zeolite - 50%

Activated Carbon - 20%

Limestone - **30%