Modifikation von natürlichem Zeolith zur optimierten Nährstoffrückgewinnung aus biogenen Abwässern

This dissertation focuses on the process-oriented optimization of natural zeolites for the simultaneous removal and selective recovery of the nutrients ammonium (NH4+) and phosphate (PO43-) from biogenic wastewater. Natural zeolites were modified to further develop an existing process (the ReNOx process) so that for both cation exchange and simultaneous anion removal from various wastewaters became possible. A standardized analytical protocol for the mineralogical and chemical characterization of natural zeolites (primarily clinoptilolite) was developed. It enables a comparative assessment of the material properties of different deposits with regard to their suitability for technical applications, particularly in ion exchange processes. The investigations included X-ray diffraction, X-ray fluorescence, thermogravimetric analysis, and electron microprobe analysis for detailed determination of mineral chemistry excluding the influence of non-zeolitic mineral accessories as they are not involved in ion exchange processes. In order to characterize the exchange capacity of ammonium in varying concentrations as they occur in biogenic waste waters exchange isotherms were determined for each zeolite sample in the range of 500 and 5000 mg L-1. In a subsequent step, various modifications using concentrated acids, bases, and salt solutions were carried out to enhance the ammonium exchange capacity. The modified zeolites were also analyzed according to the standardized analytical protocol and tested in batch (20 g) and column experiments (300 g to 2,5 kg) by using model solutions and real sludge liquor. The results showed significant improvements in ammonium uptake, particularly for NaOH-treated samples with increased sodium loading and increased specific surface area due to desilication from alkaline treatment. In parallel, strategies for phosphate removal and recovery using further modified zeolites were developed and their underlying processes were examined. For this purpose, systematic pretreatment experiments with calcium ions from various sources and concentration using a design of experiments approach were conducted. This led to the formation of sparingly soluble calcium phosphates on the zeolite surface. Phosphate removal rates of up to 94% were achieved, and recovery rates via acidic elution ranged from 73% to 82%. All developed processes were finally scaled up to pilot level and successfully tested under real-world conditions in single flow mode experiments using zeolites columns of 100 kg and flow rates up to 500 L h-1 at the wastewater treatment plant in Knittelfeld. The ReNOx-process was extended by a new phosphate module, and the application of modified zeolites in actual wastewater streams was successfully demonstrated for the first time on a larger scale. The high regenerability of the zeolites and the scalability of the process underscore its practical applicability. Additionally, further applications such as nutrient removal from pig manure and landfill leachates as well as the precocentration of green ammonia for fuel cell applications were explored. These results not only provide a substantial contribution to the use of natural zeolites in environmental technologies but also highlight their potential for sustainable nutrient recovery. Thus, this work makes an important contribution to safeguarding global agricultural resources, remediation of nutrient surplus in contaminated water bodies and advancing resource-efficient circular economy solutions.