Wastewater - Turning Problem to Solution

Source separation Source separation has been discussed under action area 2 as a strategy for eliminating contaminants prior to discharge. The use of source-separating approaches such as urine-diverting toilets merits reference again here as a decentralized wastewater treatment option. Source separation offers a radically different approach for society to manage all three challenges to the recycling of essential nutrients like nitrogen and phosphorus, inactivation of pathogens like parasitic worms and the removal of micropollutants like pharmaceuticals. Human urine contributes just 1 per cent to the volume of domestic wastewater, but contains 80 per cent of the nitrogen, 50 per cent of the phosphorous and potassium, 64 per cent (+/– 27 per cent) of the pharmaceuticals and has a very low pathogen load compared with faeces (Vinnerås 2006; Lienert, Bürki and Escher 2007). Human urine can be collected separately from faeces by using urine-diverting toilets and unisex urinals. Since the 1990s, urine separation has been practised in

contaminants, volume and intention for reuse. There are standards and standard designs based on loading, water quality and temperature which influence the choice of design. While NBS have predominantly been used for domestic wastewater treatment, there has been some application of NBS to industrial wastewater flows, including the use of constructed wetlands for dairy shed waste (WWAP 2018). NBS have been found to be cost-effective both in terms of construction and operation (WWAP, 2018). When designed and implemented appropriately, they can provide an affordable and reliable option for decentralized wastewater treatment and resource recovery for application in a range of geographic contexts, including small island developing States, such as in the Solomon Islands. At the regional scale, the Contracting Parties of the Barcelona Convention have agreed to promote the use of NBS to the extent possible for smaller communities (i.e. less than 2 000 persons equivalent) (UNEP 2021b)

Nature-based systems for wastewater treatment

Water-based systems

Substrate-based systems

Ponds

In-stream restoration

Surface ow wetlands

Ponics technologies

Soil in ltration systems

Building-based system

Willow systems Treatment wetlands (TW) dominated by willows. Used for onsite wastewater treatment and reuse Zero discharge systems

Subsurface ow wetlands

Sludge treatment

Anaerobic

Restore natural stream functions Reconstructing the natural hydrology of the stream Removing legacy sediments and planting trees/shrubs along the bank Reconnecting the channel to the ood plain

Natural wetlands Hydroponics

Slow rate

Rooftop treatment wetlands

Vertical- ow TW

Reed beds

Plants` rootsystems are used to remove nutrients

Rapid rate Controlled application of primary or secondary wastewater to a vegetated land surface A land treatment technique that uses the soil ecosystem to treat wastewater

A treatment wetland system to dewater and mineralise sludge

Vertical- ow (Vf): primary treated wastewater is intermittently loaded on the surface of the lter and percolates vertically

Intensi ed Classical: the rst and smallest units within a pond service High-rate: for advanced primary treatment of wastewater, often combined with facultative ponds or treatment wetlands Surface aerated: can use aeration to create aerobic conditions at the surface, anoxic at the bottom Facultative: wastewater stabilisation ponds designed for BOD* removal based on surface organic loading Maturation: wastewater stabilisation ponds that use natural processes to Aerobic

Floating wetlands Wetlands where the water surface is exposed to the atmosphere Wetlands with artifucial platforms which allow aquatic plants to grow in water otherwise to deep for them Free water surface wetlands E ective treatment in a passive way and minimize need for mechanical equipment, energy, and skilled labour.

Living walls Planted, vertical walls can be used to treat grey water for reuse purposes Green roofs are essentially wetland beds designed to treat wastewater for subsequent reuse

Aquaponics Aquaculture + Hydroponics = Aquaponics

by production of woody biomass

French VfTW with twi vertical stages with di erent lter media

Horizontal- ow TW Gravel beds plamted with emergent wetland vegetation promoting horzintal ow through the lter media Aerated: an advanced type of TW for more e cient removal of contaminants due to higher oxygen availability Reciprocating: coupled subsurface ow treatment cells that are recurrently lled and drained Reactive media in TW: uses media with an a nity for orthophosphate ions Intensi ed TW

polish and disinfect secondary treated wastewater

*Biochemical/biological oxygen demand

Source: Adapted from Cross et al. eds. 2021

Figure 3.9: NBS systems for wastewater treatment.

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