Using Anaerobic Baffled Reactor Effluent to Irrigate Crops

Water continues to be a limited resource. In many countries, water for direct human consumption is given priority over irrigation water. This can lead to an increase in cost for farmers. Reusing wastewater is one of the top ways to both efficiently manage this limited resource and keep costs low for farmers.

 

What is Anaerobic Baffled Reactor Effluent?

An Anaerobic Baffled Reactor (ABR) uses both settling tanks and a biological treatment to clean wastewater. Each reactor has a series of alternating hanging and standing baffles along the chamber. This design forces the flow to move from the top to the bottom within each baffled chamber.

Because the flow is forced down to where the residual sludge sits, it increases the contact with the anaerobic digestion microorganisms present in the sludge. This increases the anaerobic digestion rate of the organic pollutants and makes it more efficient than other water treatment methods. The baffles also slow down the flow and encourage settling of solids.

ABR can even generate power using the gases that are produced. Many developing countries are adopting ABR at a full-scale. However, the effluent from an ABR needs more treatment to be used in most applications – it just isn’t clean enough.

ABR Effluent for Rice Irrigation

A study by the University of KwaZulu-Nata in South Africa published in 2019, looked at the use of ABR effluent in crop irrigation – specifically when growing rice. Researchers selected rice, because it has high water and nutrient requirements that limit the potential irrigation methods. Rice is a staple crop for most of the world. Improving the yield on this crop could help improve hunger issues around the world.

Since ABR effluent is graywater and blackwater, there is a potential for health risks for consumers and farmers. Rice is a crop that always needs to be cooked before consumption – limiting these health risks. Researchers recommended that health safety standards be put in place to protect farmers, like proper PPE.

The study looked at the impact of ABR effluent using three different irrigation techniques, alternate wetting and drying (AWD), flood irrigation (CFI), and wetting without flooding (WWF). AWD simulates the natural ebb and flow of flooding conditions. With AWD, farmers wait to flood the fields until soil moisture parameters are met or until visual cues from the soil or plants indicate a lack of moisture. WWF keeps the soil as close to saturated as possible, but there is no standing water in the rice field.

CFI, when the fields are kept continuously flooded, is the conventional way of cultivating lowland rice. It is also considered to be the least efficient. CFI was used as the control in this study. These three techniques were studied using ABR effluent to better develop recommendations for farmers.

The study found that ABR effluent had a positive impact on the growth and yield parameters of lowland rice. The effluent provided all the required nutrients with no fertilizer added. Rice has always been grown using continuous flooding techniques – this study could change that. The AWD irrigation technique was the most efficient when comparing the amount of irrigation and total water use. This technique used 38 and 52% less water that CFI in 2017 and 2018, respectively. AWD also had the highest yields of the three techniques.