Project Details
| Size | 7 m³/day |
| Location | Spain |
| Completed | 2024 |
Project Delivery
| Features | Retrofitting in limited space |
| No interventions in existing tanks | |
| High time pressure | |
| Treatment Modules | ClearFox® FBBR |
| ClearFox® Clarifier |
Project Results
| Before | After | |
| SS | 300 mg/l | <10 mg/l |
| Ntot | 150 mg/l | <60 mg/l |
| Ammonium | 135 mg/l | <15 mg/l |
Discussion
Situation
In the summer of 2024, PPU Umwelttechnik GmbH was entrusted with an urgent project in Spain through its Spanish trading partner Protecnia. A cardboard factory operates its own wastewater treatment plant in the basement of its facility. The wastewater treatment plant was originally designed as an SBR (Sequencing Batch Reactor) system but was implemented as a continuous-flow multi-chamber oxidation plant with a total volume of approximately 8 m³. The plant had been modified by the operator to ensure at least basic aeration and oxygen input. During daily operation, approximately 140 people work in three shifts.
The wastewater originates mainly from sanitary facilities – toilets and hand basins – with also a minor contribution from industrial process wastewater. The original plant had long since reached its load limit, which resulted in repeated exceedances of legal discharge limits.
Problem
Initial analyses already revealed critical exceedances, particularly in nitrogen compounds:
- Ammonium (NH₄⁺): 135 mg/l (permissible: < 60 mg/l)
- Total Kjedahl Nitrogen (TKN): 150 mg/l (permissible: < 90 mg/l)
These values led to repeated complaints from the municipal water authority, which ordered the operator to promptly improve the system. In addition, blockages in the coarse filter area occurred weekly, resulting in the regular use of external vacuum trucks – with corresponding follow-up costs.
Although the existing plant was able to reduce the COD (chemical oxygen demand) to acceptable levels through its aeration, the nitrifying microflora was suppressed by the high carbon content in the influent, which severely hindered biological nitrogen conversion. In short: The system in its configuration was not capable of ensuring nitrification and denitrification.
Solution
After a detailed evaluation of the laboratory analyses, volume data, and hydraulic load, PPU Umwelttechnik GmbH developed a compact downstream solution: a two-stage biological treatment system with fixed-bed biological reactors (FBBR) and a subsequent secondary clarifier to separate the activated sludge.
Installed components:
- FBBR AP3500 as the first treatment stage for nitrifying microorganisms
- FBBR AP2250 for further ammonium conversion and possible denitrification
- AP2250 secondary clarifier with internal recirculation
- Compact control unit for regulating aeration and pump runtimes
- Sludge pump for recirculation or disposal
The entire retrofit solution was installed directly behind the existing effluent and, thanks to its compact modular design, could be integrated into the existing system without any intervention or construction work.
Just a few weeks after commissioning, the effluent analyses showed a significant improvement in all relevant parameters. Particularly noteworthy:
- Ammonium was reduced to <15 mg/l – in compliance with municipal requirements.
- TKN fell to <20 mg/l
- Solids were reduced to <10 mg/l
- The COD was further reduced from 270 mg/l to below 70 mg/l
In addition, improved sludge separation in the lamella clarifier significantly reduced maintenance requirements in the primary clarifier. The use of vacuum trucks was significantly reduced.
The customer was very satisfied with both the technical performance and the short implementation time. The project is a successful example of an intelligent, modular retrofit in which an existing system was raised to a new level of performance through targeted additions – cost-effective, space-saving, and sustainable.
