How Can We Benefit from Wasted Gray Water?

Gray water treatment is the future of the water file in all countries of the world. The areas of use of treated gray water are expanding in a number of applications. This guides the consumption of clean water and limits it to more important areas where it cannot be replaced.

Gray water is the result of water used except for toilets, specifically sink water, bath water, laundry water, kitchen water, dishwasher water, etc. However, some studies recommend not connecting the result of kitchen wastewater and dishwasher water to the gray water tank because it contains fats, oils, and food residues that make desalination difficult.

Studies have shown that gray water got its name from being intermediate water between pure, clear water, which is technically called white water, and polluted sewage water, which is also technically called black water.

Why do we care about gray water treatment?

• This water constitutes approximately 55-74% of the water used in buildings.
• It contains a low percentage of organic matter and nitrogen pollution as well as germs and microbes, and therefore it is easy to deal with during the purification stages.
• Low treatment costs compared to sewage water.
• Humans accept the reuse of this water.
• Recycling and reusing are harmless to the environment and health if the specified conditions and specifications are applied.

While statistics indicate that the percentage of gray water reaches 75% of the total water used in homes, i.e. more than half of the water we get rid of through the sewage system in homes.

Therefore, the Ministry of Environment, Water and Agriculture in our beloved Kingdom, in the implementation of the 2030 strategy, sought to benefit from this high percentage, which contributes to reducing the demand for water and developing and preserving water resources.

The following graph shows that what is treated from wastewater (gray water) ranges between 45% and 51% of the total freshwater used in the municipal sector during the years (2010: 2018 AD), according to the report of the General Authority for Statistics.

What is treated from wastewater (gray water) ranges

Despite the importance of water, the Kingdom faces major challenges due to the unsustainable use of water resources, in addition to the limited groundwater reserves, and in arid climate conditions, renewable water is scarce, noting that the high demand for water in the agricultural sector is a major cause of the water scarcity problem in the Kingdom.

The average per capita share of water in the Kingdom was estimated at about 280 liters per day in 2019, indicating a decline of 0.5% from 2018, and since the agricultural sector is the largest consumer of water in the Kingdom, accounting for 80% of the total demand for water, the sector’s consumption is growing at a rate of 7% annually.

Therefore, gray water treatment is currently receiving a lot of attention because it has low levels of polluting pathogens and nitrogen.

Gray water Treatment Methods:

Gray water treatment requires the establishment of two networks to drain sewage, the first is for draining gray water, where it is collected in a ground tank for treatment and then recycled in the flushing boxes and agriculture, and the second network is for draining blackwater.

The Gray water treatment also requires the establishment of a tank to collect the treated gray water and a feeding network for the flushing boxes and agriculture. There are several treatment methods that the designer can choose the most appropriate according to the nature of the site, provided that the treated water meets the specified conditions, standards, and requirements, in order to protect public health and the environment.

A video simplifying the idea of ​​gray water treatment

Considerations for Choosing Gray Water Treatment Technology

When choosing the treatment technology, the following criteria and considerations should be taken into account:

• The suitability of the station for the type of water to be reused.
• Determining the design capacity of the station to match the actual need for its use.
• The efficiency of the station to achieve the highest return from the treated water.
• Adherence to the specifications of the World Health Organization.
• The efficiency of the station to achieve high quality of the produced water according to the specifications of the World Health Organization and the General Presidency of Meteorology and Environmental Protection.
  The suitability of the plant for the location and number of users.
• It is low-cost, and easy to operate and maintain.

Gray Water Treatment Technologies

Physicochemical Treatment

Physicochemical treatments of gray water primarily use filtration and disinfection methods. The filtration method is effective in reducing TSS, TDS, and turbidity. Sand filters are effective in reducing TSS, TDS and turbidity levels of gray water of more than 80%.

This is because fine sand particles can remove ions (negative charge of waste colloids) using adsorption and ion exchange mechanisms. Sand also has hydrophobic properties that can interact strongly with solids such as TSS. A sand filter will also form pore layers that can trap solids. However, using a sand filter alone without any prior sedimentation steps to treat gray water will require a shorter cleaning period for the filter. A sand filter is not an effective means of reducing carbon pollutants in gray water because most of the carbon elements dissolve.

Biological Treatment

Biological treatment mainly uses aeration techniques and membrane bioreactors. Aeration technology is implemented by providing sufficient levels of oxygen in the water so that bacteria can decompose organic contaminants.

In contrast, membrane bioreactor technology combines biological treatments with physical separation of solids. One method of aeration technology is the sequencing batch reactor (SBR), which removes COD levels up to 90%. This is because most of the COD in gray water is colloidal, which is easier to decompose by
Aerobic Processes.

Advanced Oxidation Process (AOP) Treatment

AOP is an oxidative chemical technology that produces mostly hydroxyl radicals (OH*) as strong oxidants in liquid media. These OH* are highly reactive and non-selective.

MBBR Technology

One of the latest technologies used in gray water treatment to meet the needs of developing countries. And to make the central wastewater treatment plant environmentally and economically sustainable. There was a need to focus on creating a compact, highly efficient, easy-to-use, cost-effective system that is integrated with natural treatment.

Most combined treatment plants include biological unit processes as a secondary treatment to remove soluble contaminants (e.g. MBBR and MBR) in addition to wet composting tanks, vermicomposting and anaerobic treatments; sand, soil, and peat filters; wastewater; and gray and black water separation systems, after the primary treatment stage. MBBR technology has proven its technical efficiency, environmental efficiency, and economic efficiency.

You can read more about gray water treatment technologies from our article.

Benefits of treated water:

• Agricultural irrigation for agricultural crops.
• Irrigation of residential and public green spaces.
• Firefighting.
• Industrial treated water that may come into contact with workers.
• Industrial or commercial cooling or air conditioning.
• Making artificial snow.
• Afforestation in public gardens, parks, hotels, and resorts.

At CareWater Establishment, we are keen to provide the latest technologies that suit various applications. With the aim of continuous improvement and providing all water solutions. In our keenness to provide continuous support for the development of our beloved country and continuous progress.