Manure management practices on biogas and non-biogas pig farms in developing countries – using livestock farms in Vietnam as an example

Abstract

This survey was carried out to study animal manure management on livestock farms with biogas technology (biogas farms) and without (non-biogas farms) in the areas surrounding the Vietnamese cities Hanoi and Hue. The objective of the study was to assess the contribution of biogas production to a better environment as well as to recognize the problems with livestock manure management on small-scale farms. On all the farms included in the study more than one manure management technology was used, i.e. composting, separation of manure, biogas production and discharge of liquid manure to recipients such as public sewers or ponds. On biogas farms, most of the manure collected was used for bio-digestion. The farmers used the fermented manure (digestate) as a source of nutrients for crops, but on more than 50% of the interviewed biogas farms digestate was discharged to the environment. On non-biogas farms, manure was in the form of slurry or it was separated into a liquid and a dry-matter-rich solid fraction. The solid fraction from separation was used for composting and the liquid fraction usually discharged to the environment. The survey revealed that there is a need to improve methods for transporting the manure to the field, as transportation is the main barrier to recycling the liquid manure fraction. Farmers in developing countries need financial and technical support to install biogas digesters and to overcome the problems involved in utilizing the manure. Information about how to pre-treat manure before adding it to the digester is urgently needed. At present too much water is used, and the high volume of slurry reduces the retention time and is a disincentive for transporting and applying the digestate to fields. The users need to be informed about the risk of loss of methane to the environment, how to prevent cooker corrosion and the discharge to recipients. In addition, the study reveals that in developing countries manure management legislation needs to be tightened to control environmental pollution.