BIOGAS PROCESS WITH NUTRIENT RECOVERY

摘要

The invention is a method of two-phase anaerobic digestion where monitoring and adjusting the nitrogen status (carbon to nitrogen molar ratio, i.e. C/N molar ratio or total or ammoniacal nitrogen content) enables maintaining optimum conditions during the process. The method improves the use of a variety of feedstock materials or facilitates monodigestion of one feedstock. Especially the introduction of nitrogen rich feedstock materials in the process is amended. A community of hydrolyzing and acidogenic microorganisms in the first phase digester performs ammonification i.e. release of organic nitrogen as ammonia. Nitrogen and phosphorus are removed and recovered from the digestate which then undergoes biogasification in the second phase of the process. Reject water from biogasification can be recycled within the process.

主权项

1. A process for optimizing production of biogas from one or more feedstock materials, which biogas production is conducted in at least a second reactor, the process comprising,
(a) determining total elemental nitrogen (N) content in volatile solids (VS) or a carbon to nitrogen (C/N) molar ratio of the one or more feedstock materials, and (b) determining total elemental nitrogen content or total ammoniacal nitrogen content or C/N molar ratio of the contents of the second reactor, wherein the feedstock material is nitrogen rich when the C/N molar ratio of the feedstock material is below 15, or the total elemental nitrogen content in VS of the feedstock material is above 40 grams N per kilogram VS, wherein the feedstock material is carbon rich when the C/N molar ratio of the feedstock material is above 15, or the total elemental nitrogen content in volatile solids of the feedstock material is below 40 grams N per kilogram of VS, wherein the nitrogen status in the second reactor is optimal when the C/N molar ratio in reactor contents is between 5.0 and 12, or the amount of total ammoniacal nitrogen in reactor contents is between 0.1 and 2.5 grams per liter, or the amount of total elemental nitrogen in reactor contents is between 0.3 and 2.8 grams per liter, (c) when the nitrogen status determination in step (a) or step (b) indicates that the feedstock is nitrogen rich, or that the second reactor has a below optimum C/N molar ratio or an above optimum content of total ammoniacal or elemental nitrogen, treating the nitrogen rich feedstock in a first reactor with at least one ammonifying microbial species to produce an ammonia digestate, wherein an ammonia digestate is a digestate originating from the first reactor where the feedstock has been ammonified until preferably more than 50% of the total elemental nitrogen in the feedstock is converted to ammonia, (d) delivering the ammonia digestate from the first reactor to a nitrogen removal system, (e) treating the ammonia digestate in the nitrogen removal system to produce an ammonia-reduced digestate, wherein an ammonia-reduced digestate is an ammonia digestate that has passed through the nitrogen removal system to achieve removal of at least 80% of ammonia nitrogen, (f) delivering the ammonia-reduced digestate from the nitrogen removal system to the second reactor, (g) when the nitrogen status determination in step (a) indicates that the feedstock is carbon rich, delivering carbon rich feedstock directly to the second reactor, (h) when the nitrogen status determination in step (b) indicates that the second reactor has an above optimum C/N molar ratio or a below optimum content of total ammoniacal or elemental nitrogen, delivering nitrogen rich feedstock directly to the second reactor, the process further comprising (i) producing biogas from the delivered feedstock with at least one methanogenic microbial species in the second reactor, and (j) determining nitrogen status of the ammonia-reduced digestate after nitrogen removal and controlling efficiency of the nitrogen removal system and flow of ammonia-reduced digestate into the second reactor.