Hybrid SBR and Fixed Film Reactor for Selenium Removal
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Solution Overview
Problem
Fixed film reactors experience reduced performance when treating influent with high nitrate or total suspended solids (TSS) concentrations, leading to issues like poor media bed permeability, scaling, and biological toxicity, which complicates selenium removal from wastewater.
Innovation Solution
A sequencing batch reactor (SBR) process is used to reduce nitrogen and TSS concentrations, followed by a biological reduction process in a fixed film reactor to convert selenium species into elemental selenium for precipitation and removal, addressing scaling and toxicity concerns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed film reactor is used to remove selenium from wastewater, then selenium removal is achieved, but performance is reduced when treating influent with high nitrate or TSS concentrations
Solution Approach 1:
The patent applies preliminary action by implementing a sequencing batch reactor (SBR) before the fixed film reactor to pre-treat the wastewater. The SBR performs aerobic and anoxic treatments to reduce nitrate and TSS concentrations before the effluent enters the selenium-removing fixed film reactor, thereby protecting the reactor's performance from the harmful effects of high nitrate and TSS
2Quantity of substance
If high nitrate concentrations are present in the influent, then nitrogen removal is needed, but media bed permeability deteriorates due to scaling
Solution Approach 1:
The SBR performs preliminary nitrogen removal through aerobic nitrification and anoxic denitrification processes before the effluent reaches the fixed film reactor. This preliminary action prevents nitrate-related scaling in the media bed, maintaining permeability while achieving nitrogen removal
Solution Approach 2:
The treatment process is segmented into distinct functional zones: an aerobic zone for nitrification, an anoxic zone for denitrification, and a separate fixed film reactor for selenium removal. This segmentation allows each process to occur under optimal conditions without interfering with media bed permeability
3Quantity of substance
If high TSS concentrations are present in the influent, then solids removal is needed, but biological stability is compromised due to toxicity
Solution Approach 1:
The SBR performs preliminary TSS removal through settling and biological degradation processes before effluent flows to the fixed film reactor. This preliminary solids removal reduces toxicity to selenium-reducing organisms, maintaining biological stability in the downstream reactor
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
The process effectively reduces selenium concentrations in wastewater, improving media bed permeability and biological stability, and ensures compliance with discharge regulations by minimizing nitrate, TSS, and heavy metal concentrations.
Implementation Method 1
aerobic treatment to remove chemical oxygen demand and nitrify a waste stream
Implementation Method 2
anoxic treatment to denitrify a waste stream
Implementation Method 3
reducing the selenium species in the intermediary stream by means of a biological reduction process
Implementation Method 4
The elemental selenium is precipitated and removed from the water
Data Source
AI summary
A system for treating wastewater containing selenium has a sequencing batch reactor upstream of a fixed film reactor. The sequencing batch reactor may be operated under anoxic conditions while influent is mixed with residual sludge. The SBR reduces total nitrogen, suspended solids, or both. Selenium is removed in the fixed film reactor by biological reduction to elemental selenium.