Techno-Economic Assessment of On-Farm Anaerobic Digestion System Using Attached-Biofilm Reactor in the Dairy Industry

Jia Boh Tan,Zurina Zainal Abidin,Wei En Tan,Hasfalina Che Man,Nur Syakina Jamali

doi:10.3390/su13042063

Abstract

In this study, a techno-economic assessment of an on-farm biogas system using an anaerobic biofilm reactor utilizing cow manure as a fermentation substrate was evaluated. A projection model was developed using Microsoft Excel software with three outputs, the size and dimension of a bioreactor, experimental microbial kinetic studies, and the economic studies based on the experimental results. Characterization analysis of cow manure wastewater showed the total solid (TS), total volatile solid (TVS), total carbohydrate (TC), chemical oxygen demand (COD), and pH values which were 10.95 g/L, 8.65 g/L, 6.65 g/L, 57.80 g/L, and 7, respectively. Using the modified Gompertz equation for the microbial studies, it was found that, at 37 °C and 20 days hydraulic retention time (HRT), the biogas yield was 934.54 mL/gVS, the volume of biogas produced was 11.28 m3/d, and 22.56 kWh of electricity was generated. The Gompertz prediction helps to determine the optimal HRT for the system so that the microorganisms are at their optimum stage to produce biogas. The economic analysis was done, and the results illustrated that, when the rate of cow manure produced was at 55 L/day.cow, the net present value (NPV) was RM 611,936.09, with a 13% internal rate of return (IRR), 0.14 return on investment (ROI), and 7.02 years of payback period (PP). By developing a techno-economic assessment that included all the necessary parameters such as sizing of the bioreactor, microbial kinetic studies, and economics of the plant, farmers could easily implement the system into their farms. This model showed that the anaerobic digestion system utilizing an attached biofilm with cow manure as a fermentation inoculum and substrate was applicable on an industrial scale to generate electricity and reutilize to the farm, at the same time generating additional income from the production of fertilizer.

Highlights

Over the past few decades, the high reliance on fossil fuels has negatively affected the community, the people, and the environment in terms of climate change and environmental degradation
Dairy cows were commonly being fed with grass, and they already processed the food with the microorganisms in cow’s rumen, leaving cow manure with high lignocellulosic contents, including cellulose, hemicellulose, and lignin [19]
The low total carbohydrate content in cow manure was related to its lignocellulosic content, causing the cow manure to be hardly hydrolyzed by acid [15]

Summary

Introduction

Over the past few decades, the high reliance on fossil fuels has negatively affected the community, the people, and the environment in terms of climate change and environmental degradation. Malaysia has a high demand in the agricultural sector and urbanization as a developing country, resulting in poor management of the environment [1]. The quest to find renewable and sustainable energy as an alternative energy source is growing more urgently than ever as time passes. Multiple researchers have researched producing biogas from biomass as an alternative energy source [3]. Biogas consists of other gasses such as ammonia (NH3 ), hydrogen sulfide (H2 S), hydrogen (H2 ), oxygen (O2 ), nitrogen (N2 ), and carbon monoxide (CO) in small quantity [4]

Methods

Results

Conclusion