Volatile fatty acids (VFAs) produced during anaerobic digestion (AD) of organic waste are a promising alternative carbon source for various biological processes; however, their applications are limited due to the presence of impurities such as ammonium (NH₄⁺). This study investigates the potential for removal of ammonium using a naturally occurring zeolite (clinoptilolite) from chicken manure (CKM) derived VFA effluent recovered from an anaerobic membrane bioreactor (MBR). Experiments were conducted for both synthetic and actual VFA (AD-VFA) solutions, and the effects of different parameters were investigated with batch and continuous studies. It was observed that the Langmuir-type isotherm provided the best fit to the equilibrium data in the isotherm investigations carried out with the AD-VFA solution. The maximum adsorption capacity (q_m) was found as 15.7 mg NH₄⁺/g clinoptilolite. The effect of some operational parameters on process performance such as pH, initial NH₄⁺ loading and potassium ion (K⁺) concentration was investigated. The pH had a negligible effect on ammonium removal for a pH range of 3–7, while the removal efficiency of ammonium decreased with the increase of initial NH₄⁺ loading and K⁺ concentration. At the optimum conditions determined in batch experiments, the ammonium removal from synthetic and AD-VFA solutions were compared and average ammonium removal efficiencies of 93 and 94% were found in 12 h equilibrium time for synthetic and AD-VFA solutions, respectively. Overall findings indicated that clinoptilolite has excellent potential for ion exchange when combined with biological processes such as acidogenic fermentation of VFAs to purify the solution from high-ammonium content. GRAPHICAL ABSTRACT

Yellow water is a segregated domestic wastewater stream resulting from Ecological Sanitation (ECOSAN). It is mainly source separated human urine which is rich in nutrients. The potential contribution of yellow water as fertilizer to food security is considerable. The use of this potential however is related to the acceptance of the consumers towards urine based fertilizers (UBF). This work aims to assess acceptance of consumers towards UBF and urine diverting toilets (UDT) for separation of urine, through questionnaires with 444 participants from Egypt, Iraq and Turkey with different age groups, genders, educational backgrounds and occupations. The overall acceptance for UDTs and UBF was 62% and 56%, respectively. All-in-all, public opinion regarding the use of UDT/UBF is promising.