Greywater use in hydroponics

By Elias Maluleke and Annah Ndeketeya

 

Rapid urbanization has seen an increased number of people living in urban areas. This often puts pressure on available water resources and service delivery including wastewater management. To meet the water scarcity challenge, the use of greywater as an alternative water source is often recommended. Greywater refers to wastewater generated from buildings that has not come into contact with urine or faecal matter (Greywater action, 2021). In addition to water security issues, is the challenge of food security as many households struggle to put food on their tables. However, there might be a workaround solution to this. Residents can use greywater to practice urban farming and improve food availability, whilst at the same time promoting sustainable wastewater management. This can be done through hydroponic farming that saves space, conserves water and promotes fast growth.

What is Hydroponic farming?

 Hydroponics is a soilless farming system that uses water and a substrate to support plant roots.  Nutrients required for plant growth are added as a solution to the water and usually refer to this solution as “plant food” (Vertical roots, 2020). There are two main types of hydroponics, namely: Open and closed hydroponic system. An open hydroponic system is a one-way system whereby water is not circulated, there is a constant input and output of the water solution. In a closed hydroponic system, the same water solution is circulated (Johnson, 2021).

Figure 1: Open and closed hydroponic systems

What is needed for hydroponics?

There are four things needed for hydroponics:

·         Light –for plants to grow they require light, which can either be natural sunlight or artificial lighting.

·         Substrate – since hydroponics don’t make use of soil the following materials are used as a substitute: “coconut fiber, pea gravel, sand, sawdust, peat moss, perlite, and vermiculite. Or they can be man-made products such as rockwool or expanded clay pellets”

·         Water – hydroponics require water that contains less than 2% of impurities for the plants to obtain enough nutrients.

·         Nutrients – a hydroponic fertilizer that contains all the nutrients needed by the plant. For a more advanced system, users may need a total dissolved solids meter to measure the mass of the dissolved solids in the solution (Miller, 2020).

What are the advantages and disadvantages?

Advantages	Disadvantages
Higher yields	Expensive to set up
Farming can be conducted throughout the year	Time- consuming
Does not require a large area of land	Can be affected by power outages
Farming can be done anywhere	Can be affected by waterborne diseases
Uses 80 – 90% less water	High possibility of nutrient deficiencies

 

The most suitable and easiest plants to start with include: lettuce, spinach, kale and herbs like mint, oregano, rosemary. Whilst some studies have proved that greywater can be used for hydroponics without health implications (Eregno et al, 2017), it is advisable to pretreat the greywater before irrigating edible vegetables (Torres et al., 2021). Others suggested diluting greywater with an equal amount of freshwater (Gaiaca, 2020) before using it for irrigation purposes.