Co-digestion of swine excreta associated with increasing levels of crude glycerin

Marco Antonio Previdelli Orrico Junior,Stanley Ribeiro Centurion,Ana Carolina Amorim Orrico,Alice Watte Schwingel

doi:10.1590/s1806-92902016000300003

Abstract

The objective of this research was to evaluate the performance of anaerobic co-digestion of swine excreta associated with increasing doses of crude glycerin and different hydraulic retention times (HRT). A completely randomized design was adopted in a 3 × 4 factorial arrangement composed of three HRT (10, 17, and 24 days) and four crude glycerin doses (0, 5, 10, and 15 g/100 g of total solids [TS]), with four replications per treatment. The assessed parameters were: biogas production potential, reductions of volatile solids (VS), chemical oxygen demand (COD), and most probable number of total and thermotolerant coliforms. The biogas production per added VS presented quadratic effect at 17 and 24 days of HRT, with ideal doses of 5.5 and 5.9 g of crude glycerin/100 g TS, respectively. There was no difference among glycerin doses at 10-day HRT for VS reductions; however, at HRT of 17 and 24 days, there were differences, with greater reduction of 61.1% for 5 g of crude glycerin/100 g TS at 24-day HRT. The COD reduction values showed an effect among retention times, in which the 24-day HRT provided the best results. Reductions in coliforms were greater than 99%, with no difference among treatments. Addition of 5 to 6 g of crude glycerin/100 g TS with a 24-day HRT is more effective in biogas production and reduction of VS, COD, and coliforms from co-digestion of swine excreta.

Highlights

The increasing production of biodiesel has generated millions of tons of crude glycerin per year
The results of reduction of biogas production with the shortest hydraulic retention times (HRT) indicate that the amount of energy available from crude glycerin was probably not used effectively by microorganisms in a 10-day hydraulic retention time
The potential results of total solids (TS) and volatile solids (VS) were superior to those reported by Miranda et al (2012), who evaluated biogas yield from bench digesters loaded with excreta from initial, growing, and finishing phases of swine fed diets based on corn and sorghum with a 30-day HRT

Summary

Introduction

The increasing production of biodiesel has generated millions of tons of crude glycerin per year. Biodiesel is converted through transesterification reaction whereby crude glycerin is generated in approximately 10%. Recent studies on anaerobic co-digestion of glycerol and excreta from animal production have aimed to reduce the impact of excess crude glycerin and increase the potential of this process. This alternative seems to be very promising, since it allows the reduction of the hydraulic retention time (HTR) spent to achieve the same biogas production generated by using only wastes (Siles et al, 2009)

Objectives

Methods

Results