NOVELTY - Process (P1) for an anaerobic digestion of an aqueous solution, or aqueous and oil two phase system (that has a chemical oxygen demand (COD) of 30-130 kgm-3), comprises subjecting the aqueous solution, or aqueous and oil two phase system to a methanogenic stage, where: methanogenic organisms (18) produce methane by digestion of organic material in the aqueous solution, or aqueous and oil two phase system; and a liquid output (3) from the methanogenic stage is recycled at not greater than a ratio of 2:1 of recycled liquid:input aqueous solution, or aqueous and oil two phase system.    USE - The process is useful for an anaerobic digestion of an aqueous solution, or aqueous and oil two phase system to produce methane and struvite (all claimed).    ADVANTAGE - The process: reduces the COD of the output stream by more than 70-95% relative to the input solution; is a continuous process; does not recycle the liquid output from the methanogenic stage; provides the output stream, which is conveyed along flexible tubing or piping, hence prevents or minimizes struvite from building up on an inner surface of a pipe or tube (all claimed); avoids the need for an aerobic treatment, and does not require the addition of alkali or pH control, hence it is efficient and cost effective, as compared to conventional processes; provides the biogas containing methane with high yield and quality; and reduces the formation of byproducts, and loss of microorganism mass from a methanogenic anaerobic process.    DETAILED DESCRIPTION - Process (P1) for an anaerobic digestion of an aqueous solution, or aqueous and oil two phase system (that has a chemical oxygen demand (COD) of 30-130 kgm-3), comprises subjecting the aqueous solution, or aqueous and oil two phase system to a methanogenic stage, where: methanogenic organisms (18) produce methane by digestion of organic material in the aqueous solution, or aqueous and oil two phase system; a liquid output (3) from the methanogenic stage is recycled at not greater than a ratio of 2:1 of recycled liquid:input aqueous solution, or aqueous and oil two phase system; and the COD of an output stream from the methanogenic stage is reduced by more than 70% from the input aqueous solution, or aqueous and oil two phase system. INDEPENDENT CLAIMS are also included for:    (1) a process (P2) for producing struvite, comprising subjecting an aqueous spirit distillation effluent stream to the methanogenic process, where methanogenic organisms produce methane and carbon dioxide by digestion of organic material in the effluent stream, and upon exiting from the methanogenic stage of an output stream, at least a portion of the carbon dioxide is evolved from the output stream and struvite is obtained; and    (2) a process (P3) for processing a liquid material, comprising (a) subjecting the liquid material to an anaerobic digestion process, and (b) monitoring the content of at least one micronutrient, preferably at least one micronutrient metal in a methanogenic stage of the anaerobic process, where: methanogenic organisms produce methane by digestion of organic compounds present in the liquid material and may utilize the micronutrient, and an amount of the micronutrient may be added to the methanogenic stage in response to the results of the monitoring; and the step (b) comprises (b1) measuring the amount of the micronutrient in the liquid material subjected to the anaerobic digestion or in the feed to a methanogenic stage of the process, (b2) measuring the amount of the same micronutrient in the effluent from the process or from the methanogenic stage of the process, and (b3) estimating the amount of the micronutrient to be added to the methanogenic stage to sustain growth of microorganisms in the methanogenic stage based on the difference between the amount in the liquid material or feed and the amount in the effluent and on the expected growth of the microorganisms in the methanogenic stage.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of an apparatus for a continuous anaerobic digestion process.    Aqueous waste stream feed (1)    Balance tank (2)    Liquid output (3)    Methanogenic process tank (8)    Methanogenic organisms (18)