Overview of the Use of Anaerobic Digestion on Swine Farms and the Potential for Bioenergy Production in Minas Gerais, Brazil ^†

Abstract

This study provides a comprehensive panorama of wastewater treatment on swine farms in Pará de Minas, MG, focusing on the performance of the anaerobic digester technologies adopted. Considering the economic and environmental importance of swine production, wastewater treatment is critical for mitigating environmental impacts while providing renewable energy opportunities. Data compilation from the Minas Gerais Institute of Agriculture (IMA), technical visits, and physicochemical analyses were conducted. Our results indicate that the region has significant potential to increase biogas production by expanding the number of plants and improving the efficiency of existing systems. Investments in scalable technological solutions tailored for small-scale operations are essential to enhance both wastewater treatment and biogas generation. This study demonstrates the potential for new business opportunities within the biogas value chain in Brazilian agribusiness.

1. Introduction

Brazil’s annual biogas production potential is estimated at 84.6 billion cubic meters, capable of generating approximately 36.7 GW of electricity. However, only 2% of this potential is currently tapped, underlining the need for strategic investments in the sector [1]. Swine farming contributes significantly to this untapped potential, particularly in regions like Minas Gerais (MG), a leading pork producer with over 241,000 sows and a robust agroindustrial infrastructure [2]. The region of Pará de Minas, MG, is particularly noteworthy, hosting one of the state’s largest clusters of swine farms. These farms generate substantial amounts of organic waste, which, if managed effectively, could reduce environmental impacts while producing renewable energy.

Recent federal and state-level regulations, such as Law No. 14,993 [3] on sustainable fuels and Law No. 15,042 [4] on carbon markets, further highlight the opportunities for expanding the biogas industry. At the regional level, Minas Gerais approved Law No. 24,396 [5], promoting biogas and biomethane integration into the state’s energy matrix. These initiatives highlight the significant opportunities for Brazil’s agricultural sector to enhance its income and sustainability.

This study investigates swine wastewater treatment and biogas production in Pará de Minas, Brazil (19.8627° S, 44.6082° W), as a case study, focusing on the operational challenges and opportunities for integrating anaerobic digesters into existing farm infrastructures.

2. Methodology

2.1. Study Area and Data Collection

Data from 41 swine farms in Pará de Minas were obtained from the Minas Gerais Institute of Agriculture (IMA), focusing on farm size, presence of digesters, and production practices. The location of the evaluated farms is available in the study by Silva et al. [6].

2.2. Technical Visits

Visits to six farms with anaerobic digesters were conducted. The efficiency of the anaerobic digestion process will be presented in this study based on the percentage reduction of volatile solids from wastewater. Information on operational practices and equipment was collected through observations and interviews. Physicochemical analyses of wastewater samples were performed following Standard Methods [7].

2.3. Sample Collection and Analysis

Wastewater samples were collected from six swine farms equipped with anaerobic digesters, specifically from both influent and effluent streams. The efficiency of the anaerobic digestion process was assessed based on the percentage reduction of volatile solids (VS), following Standard Methods [7]. Other physicochemical parameters, such as pH and alkalinity/acidity ratio (AI/AP), were also analyzed but are not presented in this study; however, they can be consulted in Silva et al. [6]. Additionally, data on operational practices and equipment were obtained through on-site observations and structured interviews.

3. Results

Table 1. Swine farm characteristics and digester adoption rates.

Size	Total Farms	Farms with Digesters	% AD
Small (<100 sows)	8	1	12.5
Medium (100–500 sows)	15	8	53.3
Large (≥500 sows)	18	18	100%

summarizes data collected from the IMA: farm size and digester adoption rates. Pará de Minas has 40 registered swine farms. In addition, one farm from the municipality of Florestal, located on the border, was included in the study, bringing the total number of farms analyzed to 41. From these data, 66% of farms utilize AD. Anaerobic digestion is present on 100% of large farms, 53.3% of medium-sized farms, and 12.5% of small ones.

Figure 1 illustrates the technological infrastructure mostly used on the farms visited. The visits confirmed that the farms employ covered lagoon digesters (Canadian model) without heating control or internal agitation (Figure 1a). Additionally, all farms were found to have an electrostatic screen system for solid separation from wastewater before entering the digester (Figure 1b). However, none of the farms had equipment to monitor wastewater/effluent flow rates. Only one farm employed a monitoring system for biogas production, measuring the pressure exerted on the cover sheet. All farms used biogas for electricity generation with a generator set adapted for biogas utilization (Figure 1c). The efficiency of anaerobic digestion in terms of volatile solids (VS) removed from the wastewater collected varied between 31.0% and 84.6%.

All visited pig farms use biogas-powered generators to produce electricity, often achieving significant cost savings. One property reported monthly reductions of up to USD 10,000. However, due to limited monitoring practices, key operational parameters such as organic loading rate (OLR) and biogas production were not directly measured. Most farms conduct only occasional waste and soil analyses, as required by environmental regulations.

The focus remains on electricity generation for on-site use or supply to the local grid. The farms lack equipment to monitor temperature and effluent flow, preventing assessment of temperature control during anaerobic digestion. Future studies should include these measurements to better evaluate system performance.

Anaerobic digesters ranged in size from 15 m × 30 m to 42 m × 18 m, accommodating waste from both sows and finishers. Due to irregular monitoring, precise data on loading capacity and biogas yield remain unavailable.

4. Discussion

According to [8] the Midwest region of Minas Gerais, where Pará de Minas is located, is home to the largest number of swine farms in the state (39% of the total herd), highlighting the economic importance of this activity for the municipality and the region. The analysis showed that 27 farms use anaerobic digesters, representing 66% of the total. Table 1 reflects the need to increase technical knowledge and investments to implement digesters, as these challenges are often difficult for smaller farms to overcome [9]. Larger farms (≥500 sows) were more likely to implement AD systems due to technical and financial capabilities. This disparity highlights the need for targeted support to enable smaller farms to adopt biogas technology.

During the visits, it was possible to establish that the arrangements of the AD systems adopted by the farms are very similar. The covered lagoon model digester is widely used in rural areas across different regions of Brazil for treating swine wastewater [9,10]. The technologies currently adopted only allow the producer to produce heat or electrical energy. Process monitoring regarding the generation of biogas, treated wastewater, or even parameters, such as pH and residence time, was not used by the farms. The absence of these monitoring and controls can generate risks, with possible consequences such as economic losses and environmental quality [11]. The low efficiencies obtained in the AD processes may reflect the lack of process monitoring and the simplicity adopted for their operation.

These results present an overview of the use of AD in Para de Minas, MG, Brazil, and the potential for bioenergy production in this region. However, several challenges remain regarding the effective participation of the agricultural sector in biogas and its co-products’ value chain, as well as in carbon credit trading. Key challenges include the following: (i) understanding the quantity and quality of biogas produced; (ii) ensuring the quantity and quality of biomethane produced and delivered; (iii) monitoring the anaerobic digestion process to control biogas production; and (iv) mapping existing or potential biogas production points. These actions will enhance the market potential of biogas and its co-products (e.g., biomethane, biogas, biofertilizer, and carbon dioxide).

In conclusion, while anaerobic digestion presents clear economic and environmental advantages, its broader adoption in swine farming requires concerted efforts to overcome financial and technical barriers. Future studies should focus on the long-term economic impacts of biogas systems, the scalability of advanced monitoring technologies, and policy frameworks that incentivize sustainable waste management practices.