Nitrogen Recovery from Urine via Staged Nitrification
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Solution Overview
Problem
Existing methods for treating liquid waste containing nitrogen and phosphorus are inefficient in achieving complete nitrification of organic nitrogen and separate recovery of phosphates, often resulting in incomplete conversion and contamination with unwanted ions, particularly when dealing with high nitrogen content wastes like urine.
Innovation Solution
A device and method involving contact of liquid waste with a basic solid, such as carbonate or bicarbonate, to maintain a weakly basic, neutral, or acidic pH, allowing microorganisms to break down nitrogen and phosphorus aerobically, enabling separate removal of nitrate and phosphate as fertilizers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If complete nitrification of organic nitrogen is pursued, then nitrogen conversion efficiency is improved, but system stability deteriorates due to ammonia levels above 2.5 mg NH3-N/I causing instability
Solution Approach 1:
The system performs preliminary nitrification in a first reactor before the organic nitrogen concentration becomes inhibitory, then recycles the partially treated waste back to the inlet. This staged approach with intermediate recycling allows complete nitrification to occur in steps rather than one overloaded reaction zone, maintaining system stability while achieving high conversion efficiency
Solution Approach 2:
The nitrification process is divided into multiple stages with separate reactors. The first reactor handles initial nitrification, the second reactor completes the process, and intermediate recycling connects them. This segmentation allows each reactor to operate within optimal parameters, avoiding the instability caused by high ammonia concentrations in a single reactor
2Quantity of substance
If high nitrogen content waste like urine is processed, then nitrogen recovery potential is improved, but conversion rate deteriorates due to reduced conversion at higher nitrogen concentrations
Solution Approach 1:
The system performs preliminary nitrification in the first reactor before the organic nitrogen concentration becomes inhibitory, then recycles the partially treated waste back to the inlet. This staged approach allows high nitrogen loads to be processed in steps, maintaining high conversion rates while recovering maximum nitrogen
Solution Approach 2:
The intermediate recycling creates a continuous process where partially treated waste is repeatedly processed through both reactors. This continuous circulation ensures that high nitrogen content waste receives multiple treatment passes, maintaining high conversion rates throughout the process rather than in a single-pass system
3Quantity of substance
If precipitation methods using iron and aluminum salts are used to recover phosphates, then phosphate recovery is improved, but liquid quality deteriorates due to introduction of additional unwanted ions
Solution Approach 1:
The system extracts phosphates from the liquid waste stream through precipitation in the second reactor, separating them as a solid phase. This extraction removes phosphates from the liquid while allowing the liquid phase to be clarified and reused, recovering phosphate without permanently contaminating the liquid with large amounts of metal ions
Solution Approach 2:
The system discards the precipitated phosphate as a separate solid phase while recovering the liquid phase for continued use in the process. This separation allows phosphate recovery without the unwanted ions remaining in the liquid stream, as the precipitated solids are removed from circulation
4Quantity of substance
If milk of lime is added to precipitate phosphates, then phosphate recovery is improved, but nitrogen loss increases due to increased evaporation of nitrogen compounds from high pH
Solution Approach 1:
The system changes the pH management approach by using a two-reactor system where pH is controlled locally in each reactor rather than raising the overall pH of the entire waste stream. This allows phosphate precipitation to occur at controlled pH levels without causing widespread nitrogen evaporation that would result from bulk pH elevation
Solution Approach 2:
The phosphate precipitation is segregated into a specific zone (second reactor) rather than being applied system-wide. This segmentation allows pH to be elevated only where needed for phosphate recovery, minimizing the volume of liquid exposed to high pH conditions and thereby reducing nitrogen compound evaporation losses
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 approach allows for complete nitrification of organic nitrogen and separate recovery of phosphates, enabling the production of fertilizers with controlled nutrient content, suitable for use in space exploration and agricultural applications, and effectively processing high-nitrogen wastes like urine.
Implementation Method 1
microorganisms which aerobically degrade nitrogen and optionally phosphorus from the liquid waste
Implementation Method 2
whereby the pH of the waste is maintained in the weakly basic, neutral or acidic range
Implementation Method 3
nitrogen is present in the form of an organic nitrogen compound which is converted to nitrate
Implementation Method 4
Other common methods include the precipitation of macronutrients
Implementation Method 5
DE 101 27 545 A1 discloses a method and device for the further purification of phosphates
Data Source
Figure 1
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AI summary
The invention relates to a method and an apparatus for treating liquid residual material that contains nitrogen and optionally phosphates. The aim of the invention is the targeted production of fertilizers.