Biogas Production of Pig Manure with Water Hyacinth Juice from Batch Anaerobic Digestion

Abstract

Anaerobic digestion, a series of processes in which micro-organisms break down biodegradable materials in the absence of oxygen, is normally used for wastewater treatment and energy production. Anaerobic digestion has been applied to hog – wastewater treatment and biogas production in the Mekong Delta of Vietnam, where a high percentage of the population works in the agricultural sector. However, the supply of pig manure for operating the anaerobic digesters is not always available. Therefore, to stimulate the application and operation of anaerobic digesters that are very significant to water-pollution prevention in the Mekong Delta, there is a need to find supplemental inputs to pig manure to help maintain the operation of the digesters.

The aim of our research was to find out the yield of biogas produced from batch anaerobic digestion by using water hyacinth (WH) – a plant commonly grown in the canal networks in the Mekong Delta – as a supplemental source to pig manure in biogas digesters. We conducted experiments using 50 L plastic bags of pig manure (PM) mixed with three different types of WH (C1, WH juice after 2 days of hydrolysis; C2, WH juice after 2 days of hydrolysis  +  chopped WH; and C3, WH juice after 2 days of hydrolysis  +  crushed WH). Based upon the organic dry matter (ODM) of input sources, we set up 13 experiments (with three replicates for each experiment) of 100% PM; 75% PM  +  25% WH; 50% PM  +  50% WH; 25% PM  +  75% WH; and 100% WH. The produced biogas volume was recorded daily while other parameters of pH, buffer capacity, biogas components (CH₄, CO₂, O₂, and H₂S) were recorded once daily for 7 consecutive days during the 35 day period.

According to our experimental conditions, the various preparations of WH showed differences in gas production. The gas production from experiments with C2 and C3 was not significantly different. Meanwhile, the gas production from experiments with C1 and C2 was significantly different.

With respect to C2 treatments, on the one hand, the total gas production tended to be higher in the treatments with high percentages of WH (231 L, 315 L, 392 L, 358 L, and 439 L in the treatment of 100% PM; 75% PM  +  25% WH; 50% PM  +  50% WH; 25% PM  +  75% WH; and 100% WH, respectively). On the other hand, total biogas yield per kg ODM of input materials reached the highest value in the treatment of 50% PM  +  50% WH (122 L, 148 L, 176 L, 153 L, and 171 L in the treatment of 100% PM; 75% PM  +  25% WH; 50%PM  +  50% WH; 25% PM  +  75% WH; and 100% WH, respectively).

These results strongly confirm that the farmers in the Mekong Delta of Vietnam can use water hyacinth as a potential supplement to pig manure in anaerobic digestion in case they do not have enough pig manure for their anaerobic-digestion treatment systems.