Wastewater Nitroaromatic Degradation via Pre-Reduction and Wet Oxidation
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Solution Overview
Problem
Existing methods for treating wastewater containing nitroaromatics and nitrohydroxyaromatics are costly, require high pressures and temperatures, or generate harmful byproducts, making them unsuitable for efficient degradation and safe discharge into biological effluent treatment plants.
Innovation Solution
A two-stage method involving pre-reduction with inexpensive, non-salt-forming reducing agents like peat, lignite, or hard coal under reducing conditions, followed by acidification and iron-catalysed wet oxidation with oxygen, effectively degrades nitroaromatics and nitrohydroxyaromatics without increasing salt loads or forming harmful nitrite.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If high pressure and temperature are used to degrade nitroaromatics, then degradation efficiency is improved, but operating costs and equipment complexity increase
Solution Approach 1:
The invention changes the chemical parameters of the wastewater by adjusting pH to alkaline conditions (pH 9-13) and using specific reducing agents, transforming the degradation process from requiring high pressure/temperature to operating at ambient or mild conditions. This parameter change resolves the contradiction by achieving effective degradation without complex high-pressure equipment.
Solution Approach 2:
The invention introduces intermediary substances (reducing agents like sulfite, sulfide, or iron compounds) that mediate the degradation process. These intermediaries enable nitroaromatic degradation through chemical reduction and subsequent oxidation pathways, eliminating the need for direct high-energy input and complex equipment.
2Manufacturing precision
If nitric acid treatment is used to reduce nitrohydroxyaromatics, then degradation efficiency is improved, but nitrate load in wastewater increases
Solution Approach 1:
The invention converts the harmful nitro groups into beneficial ammonium nitrogen through reduction. The nitroaromatics are reduced to aniline derivatives, which are then oxidized to yield ammonium ions - a form of nitrogen that is less harmful and can be readily assimilated by biological treatment systems, transforming a toxic substance into a beneficial nutrient.
Solution Approach 2:
The invention changes the chemical pathway from oxidation (nitric acid) to reduction-oxidation sequence, altering the transformation parameters. By using reducing agents first to convert nitro groups to amino groups, then oxidizing under controlled conditions, the process achieves degradation without generating high nitrate loads.
3Manufacturing precision
If hydrogen peroxide is used as oxidizing agent, then degradation efficiency is improved, but reagent costs and sludge production increase
Solution Approach 1:
The invention replaces expensive hydrogen peroxide with cheaper, readily available reducing agents such as sulfite, sulfide, or iron compounds. These inexpensive reagents achieve the same degradation effect through alternative chemical pathways, significantly reducing reagent costs and eliminating the need for costly oxidizing agents.
Solution Approach 2:
The invention enables the wastewater treatment system to use its own components (dissolved oxygen from air, naturally present metal ions) as oxidizing agents. The process utilizes atmospheric oxygen and trace metals in the wastewater to complete the oxidation step, eliminating the need for external addition of expensive chemical oxidants.
4Manufacturing precision
If supercritical conditions are used for thermal degradation, then degradation efficiency is improved, but operating costs and energy consumption increase
Solution Approach 1:
The invention fundamentally changes the operational parameters from supercritical conditions (high temperature and pressure) to ambient or mild conditions. By using chemical reduction-oxidation pathways instead of thermal degradation, the process achieves effective treatment at temperatures and pressures comparable to conventional wastewater treatment, dramatically reducing energy consumption.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method achieves complete degradation of nitroaromatics and nitrohydroxyaromatics, reducing nitrite levels and allowing safe discharge into biological treatment plants, while being economically favorable and avoiding the use of costly reagents or hazardous conditions.
Implementation Method 1
in a first stage, the wastewater is combined with an organic reducing agent, which is non-salt-forming in the wastewater, and is treated under reducing conditions
Implementation Method 2
the wastewater obtained from the first stage is then acidified in a second stage and oxidised with an oxidising agent
Implementation Method 3
iron-catalysed wet oxidation with oxygen
Data Source
AI summary
The invention relates to a method for treating wastewater containing nitroaromatics and nitrohydroxyaromatics, as for example arises in the production of nitroaromatics or in the production of nitrohydroxyaromatics, by a two-stage method consisting of pre-reduction and wet oxidation.