NOVELTY - Converting biomass into biogas and agricultural fertilizer comprises: anaerobic microbially digesting biomass and producing gaseous methane comprising effluent, and aqueous effluent comprising e.g. ammonia and methane; subjecting aqueous effluent in a struvite forming to low pressure, and discharging gaseous stream comprising carbon dioxide and methane to form struvite-solids; separating and collecting struvite-solids to obtain aqueous struvite poor effluent; and producing first renewable agricultural fertilizer composition by subjecting the poor effluent to aerobic microbial nitrification.    USE - The method is useful for converting biomass into biogas and renewable agriculture fertilizer.    ADVANTAGE - The method: excludes any denitrification treatment (claimed), thus keeping nitrogen compounds which would escape from cycle and lost for use as fertilizer; allows carbon dioxide elimination, thus there is no need for alkaline additions; avoids discharging ammonia into environment and converts to high end product; exhibits specific flexibility and efficiency in product cycle; reduces hydrogen sulfide release to the environment, thus reducing undesired smell associated with biomass conversion, preferably from livestock byproducts, and increasing the methane content in the biogas; conveniently converts hydrogen sulfide into sulfuric acid, that turns out useful in producing liquid soil fertilizer; provides a renewable soil fertilizer composition that is ready to use; utilizes hydrogen sulfide derived from anaerobic microbial digestion, thus producing more closed production cycle, minimizing external supply of dangerous chemicals such as sulfuric acid and handling moments of operators, and increasing intrinsic safety; provides phosphorus-sulfur fertilizer having higher phosphorus content (at least 50 wt.%) and lower potassium levels (least 50 wt.%) and nitrogen:phosphorus;potassium at 6:29:0 and minimizes biogas production waste streams.    DETAILED DESCRIPTION - Converting biomass into biogas and agricultural fertilizer comprises: anaerobic microbially digesting biomass and producing at least a gaseous methane comprising effluent, and aqueous effluent comprising phosphorus containing compounds, magnesium ions, ammonia, carbon dioxide and methane; subjecting the aqueous effluent in a struvite forming to low pressure, and discharging gaseous stream comprising carbon dioxide and methane from the aqueous effluent to form struvite-solids; separating and collecting the struvite-solids from aqueous effluent to obtain aqueous struvite poor effluent; producing at least a first renewable agricultural fertilizer composition by subjecting the poor effluent to aerobic microbial nitrification to convert at least part of the ammonia into ammonium nitrate, where first fertilizer composition is collected and transferred to storage, either directly or following a further processing. An INDEPENDENT CLAIM is also included for a system for converting biomass into biogas and renewable agricultural fertilizer, comprising: an anaerobic digestion unit for the anaerobic microbial conversion of biomass into biogas, where the anaerobic digestion unit comprises at least a digestion inlet for receiving biomass, a first digestion outlet for discharging the methane comprising gaseous effluent, and a second digestion outlet for discharging the aqueous effluent comprising phosphorus, nitrogen and magnesium, and carbon dioxide and methane, and anaerobic methane forming microorganisms; a struvite forming reactor comprising at least a struvite formation inlet for receiving the processed aqueous effluent from the anaerobic digestion unit, where the struvite formation inlet being connected to the second digestion outlet and a first struvite formation outlet for discharging a gaseous stream comprising carbon dioxide and methane, and the reactor is provided with means for subjecting the processed aqueous effluent from the anaerobic digestion unit to low pressure, and the struvite forming reactor provides struvite solids; a nitrification reactor for aerobic microbial conversion of ammonia into ammonium nitrate comprising at least a nitrification inlet for receiving the aqueous struvite poor effluent derived from the struvite forming reactor and a nitrification outlet for discharging nitrified processed renewable agricultural fertilizer composition, where the nitrification reactor comprises at least one aerobic nitrifying microorganism; and a fertilizer storage unit for fertilizer composition derived from nitrification, where the storage unit comprises at least a storage inlet for receiving fertilizer composition discharged from nitrification outlet and storage inlet is connected to the nitrification outlet.