2.2. Experimental set-up
A low-cost pilot plant (800 soles; 200 euros) was built with recycled materials in the farm under study. It consists of three anaerobic digesters (PVC containers) of 225 L total volume, without heating or agitation, which are operated in batch mode. Each digester is connected to a gas meter, as shown in Fig. 1. Temperature was monitored with a thermometer submerged in the liquid phase. Samples for pH control were taken from a sampling port placed at the bottom of each digester. A greenhouse was built to enclose the digesters in order to increase environmental temperature and avoid temperature fluctuations overnight.