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.

  

Sustainable Stormwater Management

By Phumlile Kunene and Annah Ndeketeya

Modern society has brought about rapid urbanization in many areas across the globe. This often comes bundled with various environmental problems, including water pollution mainly due to straining or insufficient service infrastructure; Urban floods are worsened by the high proportion of impervious surfaces and increased stormwater volumes. Stormwater refers to water that flows on the surface after rain. It flows off the land into storm sewers, streams, nearby lakes or rivers. As the rate of urbanization increases, the quantity of stormwater runoff also increases. Several municipalities face significant problems from combined sewer overflowing, contaminating the surface water sources during heavy rainfall events. As stormwater travels over the land, it collects considerable quantities of pollutants such as grease, fertilizers, and pesticides and deposits them in the receiving waters. Citizens and industries also contribute to stormwater pollution by improper disposal of lawn clippings, used oil and littering. These pollutants end up in stormwater drainage systems, creating danger as they become blocked in rainy seasons, resulting in flooding (Kandiah et al., 2017). With these challenges in mind, it is imperative to improve the resilience of water infrastructure to future climate extremes and exogenous factors through sustainable stormwater management.

A stormwater drain blocked by litter in Phomolong, Tembisa, Gauteng.

First and foremost, there is a need to raise awareness and educate communities on reducing damage and protecting the existing drainage infrastructure. There are various strategies that communities can engage in to ensure sustainable management of drainage systems. Doing so will complement the various infrastructure upgrading and rehabilitation programs implemented by the municipalities or responsible authorities. 

Some of the community engagement activities include:

·         Having a proper waste management

·         Replace old stormwater pipes

·         Repair damaged drainage channels.

·         Community surveillance to report illicit dumping and discharges

·         Report damaged drain water systems to the local municipality

Additionally, sustainable drainage systems (SuDS) can be implemented at the property or community level by homeowners, local business owners, churches, schools, and colleges.

 

What is Sustainable Urban Drainage Systems (SUDS)?

Sustainable urban drainage systems are an alternative approach to manage stormwater retention effectively. By definition, SUDS are a suite of technologies and techniques that address urban drainage as part of the natural water cycle through biofiltration, infiltration, groundwater recharge and sustainable storage near the collection point (Fletcher et al. 2015). 

 

Examples of (SUDS) that can be implemented.

Kabrioah irrigation using rainwater harvesting in Kempton Park Source: https://www.sahomesguide.co.za/427-kabrioah-irrigation Rainwater harvesting: A means of rainwater for storage and use for gardening, toilet flushing, and laundry.

Green roof vegetation Life Science the building at the University of the Western Cape main campus Source: https://www.uwc.ac.za/files/images/main-campus-life-sciences.jpg Green roofs: Roof which is covered with an impermeable membrane and a growing medium planted with growing plants

Porous pavement with grass in between the pavement Source: https://www.urbangreenbluegrids.com/measures/porous-paving-materials  Porous pavements: Paved surface which allows free of surface water which then drains directly into the subsoil

Natural wetland with vegetation Source:http://www.spencenursery.com/Index/stormwater_treatment_wetlands.php Natural and constructed wetlands can be effective systems for improving water quality. Wetlands store runoff water in shallow pools that support the growth of plants in the wetland

Source: https://www.slideshare.net/mapistry/municipal-stormwater-program Detention basins/ Dry ponds: Surface storage basin that provides flow control through detaining stormwater for a couple of hours.  Retention ponds/ Wet ponds: An artificial pond with vegetation around and includes permanent water, it is used to store and manage stormwater runoff

Bioswales Source: https://www.owp.csus.edu/lid/site/lot-7-infiltrating-bioswale.html Bioswales allow rainwater to soak into the soil slowly, rather than flooding the streets. They are common along streets or around parking lots. They are vegetated and also serves as biofilters.

  

Benefits of SUDS

• Help manage environmental impacts at the source rather than downstream
• Manage water runoff rates, reducing the impacts of urban generated flooding and damage to property
• Protect and enhance water quality
• Encourage natural groundwater recharge
• Pollution reduction
• Protects health, welfare and safety of the public, property from flooding
• Protects the natural environment
• Provides habitats for wildlife
• Enhance the level of attractiveness of urban areas by green infrastructure
• Contributes to tourism economic activity through pleasing aesthetics for recreational areas and job creation