15 April 2024

RichWater Sequencing Batch Reactor for domestic wastewater treatment

Author/Compiled by
Pilar Zapata (Bioazul S.L.)
Alejandro Caballero (Bioazul S.L.)

Executive Summary

RichWater® Sequencing Batch Reactor (SBR) is an activated sludge where the treatment effluent is supposed to be reused for irrigation in agriculture. So different than in “conventional” Sequencing Batch Reactors nutrients are deliberately not removed but maintained to further fertigate the crops.

Like for other types of SBRs the process can be operated in batches, with the different required conditions being established in five successive operation phases in the same reactor: fill, react, settle, draw, and idle (TOPRAK, H. 2005). At least two tanks are needed for the batch mode of operation, as continuous influent needs to be stored during the operation phase. Small systems may consist of only one tank.

SBR systems are suited for low flows because the size of each tank is determined by the volume of wastewater produced during the treatment period in the other tank (UNEP/WHO/HABITAT/WSSCC 2004). Generally, this technology can achieve pollutant removal efficiencies of: BOD5: 95%, COD: 90%, TSS: 95%, Pathogen: N/A.


Input/Output/Removal of

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Input: Raw domestic wastewater (blackwater) Industrial wastewater
Output: Secondary treated effluent Tertiary treated effluent and/ot disinfected effluent
Disinfected effluent for irrigation Disinfected effluent for fertigation (nutrient rich)


Removal of...

Total suspended solids (TSS) NH4-N Ntot Organic compunds/COD/BOD5/TOC


Design considerations

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RichWater® SBR is an activated sludge system with the peculiarity that the degradation of the contaminants and the settling take place in a single reactor, in separate phases (“batches”). Like for other SBRs, also this type of system is operated in one or several cycles consisting of the following five phases also illustrated in Fig. 1 below.

  • Filling: during the first phase of the cycle, the wastewater is introduced into the sequencing reactor.
  • Reaction: during this phase, the organic matter and nutrients contained in the wastewater are degraded. Intermittent aeration can be provided, thus, combining different conditions (aerobic, anoxic, and anaerobic).
  • Settling: during this phase, aeration and mixing in the reactor are interrupted so as to create favourable conditions for the settling of the activated sludge.
  • Emptying: once the clarified wastewater has been separated from the sludge blanket at the end of the settling process, it is removed from the reactor.
  • Inactive phase: this is an optional phase.

Sludge removal can take place at the end of the reaction phase, or during the settling, emptying or inactivity phases.

The duration of each phase and of the complete treatment cycle is programmed according to the water purification objectives pursued. Likewise, the operational cycles can be modified according to the characteristics of the influent and the quality requirements imposed on the effluent.

BIOAZUL 2014. Schematic diagram of the functional cycle of a SBR

Figure 1. Schematic diagram of the functional cycle of a Sequencing Batch Reactor (SBR). Source: BIOAZUL S.L. (2014)



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This technology is specifically applicable for treating urban and industrial wastewater or high-load industrial effluents – with the particular aim to reuse the treated effluent for agricultural irrigation. Like other SBRs it is a compact modular system, they are appropriate for sites with limited area available or locations that require decentralised wastewater management like small communities, detached homes, or remote locations. Being compact and also installable underground, SBRs have a very limited visual impact. SBRs offer treatment a wide range of treatment capacities between 4 to 2,000 population equivalent and due to their “flexibility” in their operation mode(s) they can be configured for nutrient recovery.

It is important to note that SBRs are generally susceptible to hydraulic fluctuations and shock-loads; they require continuous power supply and for maintenance purposes need to be accessible for trucks beyond the construction period.


Experiences Globally

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Due to the novelty of this approach, at the time this factsheet was written, also globally there was no example known to the authors of a RichWater® Sequential Batch Reactor (SBR) application Still relevant experiences were made by Bioazul S.L using a similar approach for a Membrane Bioreactor (MBR) treating water from a sewage treatment plant (STP) located at Algarrobo, Malaga (Spain). The capacity of the STP is around 6.000 m3/day, serving an equivalent population of 23.970 pe, while the RichWater® MBR capacity is 150m3/day. For the RichWater® MBR a Membrane Bioreactor , a mixing module to obtain the optimum combination of conventional and reclaimed water, and a sensor-based control and monitoring system are combined (Lorenzo Lopez et al. 2021 and Munoz Sánchez et al. 2018).

A few selected application examples of the more commonly used and proved conventional SBR systems are:

  • Sequential Batch Reactor (SBR) based Sewage Treatment Plant (STP) located at Aduna, Guipuzcoa, Spain. The capacity of the STP was 28.080 m3/day, increasing in rainy season up to 128.000 m3/day, serving an equivalent population of 115,317 corresponding to the municipalities of Legorreta, Amezketa, Abaltzisketa, Baliarrain, Orendain, Ikaztegieta, Alegi, Altzo, Belauntza, Ibarra, Tolosa, Hernialde, Anoeta, Irura, Asteasu, Zizurkil, Villabona, Aduna and Andoain, including waters of industrial origin (ACCIONA n.d.a).
  • Upgrade of existing Sewage Treatment Plant (STP) in Blackmans Bay, Kingborough, Tasmania to increase treatment capacity from 4.1 million litres per day to 8.5 million. It implies the combination of a wastewater treatment process called Extended Intermittent Settling Aeration (IDEA) with Sequential Batch Reactor (SBR) technology to provide a cost-effective way to treat wastewater (ACCIONA n.d.b).

Sequential Batch Reactor (SBR) based Wastewater Treatment Plant (WWTP) located at Salteras, Seville (Spain). SBR treatment system designed and built to treat the entire flow produced in an industrial slaughterhouse, with a treatment capacity of 150 m3/d. This is part of a complete system aimed to recover and recycle nutrients from slaughterhouse wastewater in the framework of a Circular Economy model. Nutrients recovered are turned into value added products for the agricultural sector (Bioazul S.L. n.d.).


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