The supply of food to the growing world population requires an increasing amount of nitrogen fertilizers, which can be achieved both by the energy-intensive Haber–Bosch process and by recovering ammonium from wastewater. Within the scope of this work, it is investigated to what extent different clinoptilolites (CLIs) can be used as ion-exchangers for the removal of ammonium from highly concentrated solutions. To this end, finely ground CLIs with different grain sizes (EcoZeo 20 and CCP 20: 0–20 µm, Micro 200: 0–200 µm) were tested for their sorption properties by varying the parameters of the sorption solution (c₀ = 1000 mg NH₄-N/L) such as pH, temperature, or contact time. All three CLIs tested were effective at adsorbing ammonium. In a pH range from 2 to 8, all CLIs were able to eliminate ammonium equally well. Furthermore, a contact time of 60 min was sufficient to achieve 84–88% of the maximum load. At a temperature of 34 °C, the highest loading was achieved (investigated range: 10–34 °C), indicating that the adsorption process of all CLIs was exergonic and endothermic. Especially for wastewater streams with high ammonium concentrations such as sludge water from wastewater treatment plants, CLI proved to be suitable to adsorb ammonium.

Sludge water (SW) arising from the dewatering of anaerobic digested sludge causes high back loads of ammonium, leading to high stress (inhibition of the activity of microorganisms by an oversupply of nitrogen compounds (substrate inhibition)) for wastewater treatment plants (WWTP). On the other hand, ammonium is a valuable resource to substitute ammonia from the energy intensive Haber-Bosch process for fertilizer production. Within this work, it was investigated to what extent and under which conditions Carpathian clinoptilolite powder (CCP 20) can be used to remove ammonium from SW and to recover it. Two different SW, originating from municipal WWTPs were investigated (SW1: c₀ = 967 mg/L NH₄-N, municipal wastewater; SW2: c₀ = 718–927 mg/L NH₄-N, large industrial wastewater share). The highest loading was achieved at 307 K with 16.1 mg/g (SW1) and 15.3 mg/g (SW2) at 295 K. Kinetic studies with different specific dosages (0.05 g_CLI/mg_NH4-N), temperatures (283–307 K) and pre-loaded CCP 20 (0–11.4 mg/g) were conducted. At a higher temperature a higher load was achieved. Already after 30 min contact time, regardless of the sludge water, a high load up to 7.15 mg/g at 307 K was reached, achieving equilibrium after 120 min. Pre-loaded sorbent could be further loaded with ammonium when it was recontacted with the SW.

The zeolite clinoptilolite (CLI) is known to be a very good ion exchanger, as it consists of a three-dimensional structure formed of AlO₄⁻ and SiO₄ tetrahedral, which are connected by a common oxygen atom. The micropores formed by this structure (with free diameters in the range of 0.40 nm and 0.72 nm) are fine enough to allow cations and water molecules to enter and be exchanged. CLI is a suitable, inexpensive, and globally available material for removing ammonium from highly-concentrated wastewater and is proven to be selective in ammonium uptake and regeneration since no effect of the provenance of the ammonium (matrix-free NH₄Cl solution or sludge water) could be found. However, regeneration of the clinoptilolite is necessary to recover the adsorbed ammonium for further use and restore its capability for ion exchange. Within this work, the method by which clinoptilolite, loaded with ammonium (q = 8.1–16.6 mg/g) from different sludge waters and ammonium chloride solution, can be regenerated to yield a stoichiometric ammonium sulfate solution (ASS), that could be used, e.g., as a fertilizer, was investigated. A regeneration solution containing Na₂SO₄ (0.25 n(Na₂SO₄)/n(NH₄⁺_ads)) with a varying NaOH ratio (0–2.14 n(NaOH)/n(NH₄⁺_ads)) was tested. To obtain a high ammonium concentration in the eluate, a large mass fraction ω of 284 g/kg of CLI in the regeneration solution was applied. The effects of different ammonium loads, different origins of the ammonium, and residual moisture on the necessary components of the regeneration solution, in which an ASS is obtained within a contact time of 10 min at 22 °C, were studied. A stoichiometric ASS from CLI loaded up to a maximum of 13.5 mg/g was obtained with a mixture of 0.25 n(Na₂SO₄)/n(NH₄⁺_ads) together with 0.8–1.0 n(NaOH)/n(NH₄⁺_ads) for dry CLI, and 0.75 n(NaOH)/n(NH₄⁺_ads) for CLI with residual moisture.

Discharge of toxic industrial wastewaters into biological wastewater treatment plants may result in inhibition of activated sludge bacteria (ASB). In order to find an appropriate method of detoxification, the wastewater of a pesticide-processing plant in Vietnam was treated with three different methods (Fe^III, powdered activated carbon (PAC), Fenton (Fe^II/H₂O₂)) analyzing the detoxification effect with the nitrification inhibition test (NIT), respiration inhibition test (RIT) and luminescent bacteria test (LBT). The heterotrophic ASB were much more resistant to the wastewater than the autotrophic nitrificants. The NIT turned out to be more suitable than the RIT since the NIT was less time-consuming and more reliable. In addition, the marine Aliivibrio fischeri were more sensitive than the nitrificants indicating that a lack of inhibition in the very practical and time-efficient LBT correlates with a lack of nitrification inhibition. With 95%, the Fenton method showed the highest efficiency regarding the chemical oxygen demand (COD) removal. Although similar COD removal (60–65%) was found for both the Fe^III and the PAC method, the inhibitory effect of the wastewater was reduced much more strongly with PAC. Both the NIT and the LBT showed that the PAC and Fenton methods led to a similar reduction in the inhibitory effect.

In Vietnam existieren über 200 registrierte Industriezonen, die meisten bisher ohne funktionierendes Abwasserkonzept. Dezentrale Vorbehandlungsanlagen in Unternehmen sollen den störungsfreien Betrieb einer zentralen mechanisch-biologischen Kläranlage ermöglichen.