Optimization of nitrogen removal from piggery waste by nitrite nitrification

Area of Science:

• Environmental Engineering
• Wastewater Treatment
• Microbial Processes

Background:

• Piggery waste characteristics vary significantly based on manure collection and water usage.
• Waste strength, indicated by the Chemical Oxygen Demand to Total Kjeldahl Nitrogen (COD/TKN) ratio, differs between well-separated solids (ratio ~4) and mechanically scraped solids (ratio ~7).

Purpose of the Study:

• To determine optimal operating conditions for nitrogen removal from piggery waste using nitrite nitrification.
• To evaluate the efficiency of nitrite nitrification and denitrification processes for reducing oxygen and carbon demands.

Main Methods:

• Investigated nitrogen removal efficiency under varying COD/TKN ratios (4 and 7).
• Assessed the impact of nitrogen loading rate and pH on stable nitrite nitrification.
• Examined requirements for complete denitrification, including influent COD/TKN ratio and oxic/total reactor volume ratio.

Main Results:

• Nitrogen loading rate and pH are critical for stable nitrite nitrification.
• Applicable nitrogen loads range from 0.3 to 2.0 kgTKN/oxic m3/d for high COD/TKN ratios without pH control.
• Higher pH (>8) increased NO2N/NOxN ratios; low COD/TKN ratios (<4) required additional alkalinity.
• Complete denitrification requires influent COD/TKN > 6 and an oxic/total reactor volume ratio of 0.5.

Conclusions:

• Nitrite nitrification and denitrification offer substantial savings in tank volume (35%) and carbon requirements (50%).
• A 9.5% oxygen saving is achievable with low COD/TKN ratios.
• Elevated temperatures enhance microbial activity but require careful monitoring to avoid inhibiting nitrification.