Post-treatment of high-rate activated sludge effluent via zeolite adsorption and recovery of ammonium-nitrogen as alternative fertilising products.

This study investigates the potential to connect nutrient flows between wastewater treatment and agriculture through a two-stage nitrogen (N) recovery system composed of high-rate activated sludge treatment in contact stabilisation mode (HRAS/CS) and column adsorption with zeolite. The HRAS/CS process removes organic matter and suspended solids in wastewater, leaving N behind in the effluent. The N was successfully recovered with the zeolite column under different scenarios, generating N and K-rich by-products. The regeneration effluent from the zeolite column with KCl contained 60-845 mg NH4+-N/L and 1.6-14.3 g K/L, having potential for use as fertigation water. The N-saturated zeolite contained 1.5-8.4 mg N/g and 14.3-19.3 mg K/g of the product fresh weight and low contaminant content, making it potentially eligible as various fertilising products. Adsorption can thus concentrate N from HRAS/CS effluent and produce by-products with potential agricultural value while meeting chemical oxygen demand and total nitrogen discharge standards.

Enhancing swine manure treatment: A full-scale techno-economic assessment of nitrogen recovery, pure oxygen aeration and effluent polishing.

In regions with intensive livestock production, managing the environmental impact of manure is a critical challenge. This study, set in Flanders (Belgium), evaluates the effectiveness of integrating process intensification measures into the treatment of piggery manure to mitigate nitrogen (N) surplus issues. The research investigates the techno-economic benefits of implementing three key interventions: pure oxygen (PO) aeration, ammonia (NH3) stripping-scrubbing (SS) pretreatment, and tertiary treatment using constructed wetlands (CW), within the conventional nitrification-denitrification (NDN) process. Conducted at a full-scale pig manure treatment facility, our analysis employs steady-state mass balances for N and phosphorus (P) to assess the impact of these process intensification strategies. Findings indicate that the incorporation of advanced treatment steps significantly enhances the efficiency and cost-effectiveness of the manure management system. Specifically, the application of PO aeration is shown to reduce overall treatment costs by nearly 4%, while the addition of an NH3 SS unit further decreases expenses by 1-2%, depending on the counter acid utilized. Moreover, the implementation of a CW contributes an additional 4% in cost savings. Collectively, these measures offer substantial improvements in processing capacity, reduction of by-product disposal costs, and generation of additional revenue from high-quality fertilising products. The study highlights the potential of advanced treatment technologies to provide economically viable and environmentally sustainable solutions for manure management in livestock-dense regions, emphasizing the cumulative economic benefit of a holistic approach to process intensification (10%).

Development of conversion factors to estimate the concentrations of heavy metals in manure-derived digestates.

During biogas production, a residual by-product rich in organic matter, nutrients, and trace elements - called digestate - is generated. Due to the nature of the anaerobic digestion process (i.e., conversion of organic matter into biogas) and the non-digestibility of trace elements, metal concentrations are higher in digestate than initially in the treated feedstock, resulting in a detrimental effect on the environment when directly applied as fertiliser on the soil. This study aims to predict the concentration of heavy metals in digestate through four different process parameters (Biogas yield - M1, Biodegradable fraction - M2, Dry matter - M3 and Power generation - M4) in full-scale biogas plants. For the validation of the process parameters, the predictions were compared against laboratory analyses of feedstocks and digestates samples from mono- and co-digestion processes. The convergence between the conversion factors based on laboratory data and process parameters (CLD and CFA, respectively) ranged in the following order: M3 > M2 > M1 > M4. Based on laboratory analyses, better predictions were obtained for Al, Cr, Cu, Fe, Mn, and Zn employing M3. Moreover, a robust convergence was achieved between the CLD and CFA conversion factors for the mono-digestion process. Further assessment of a diverse range of feedstocks is needed to increase the convergence between the conversion factors based on process parameters and laboratory data, specifically for the co-digestion process M3. The concentrations of Cd, Co, Ni, and Pb elements were below the detection limits, whereas Cr, Cu, and Zn did not exceed the legal threshold limits of the legislations.

Impact of time and phosphorus application rate on phosphorus bioavailability and efficiency of secondary fertilizers recovered from municipal wastewater.

Demand for phosphorus (P) resources other than non-renewable P rock has driven the development of several P recovery technologies from municipal wastewater treatment and directed recovery of P into valuable fertilizers (struvite, ash, iron phosphate, etc.). Although the bioavailability of novel secondary P fertilizers has been examined in previous studies, insufficient attention has been paid to defining optimal plant growth duration and monitoring conditions to assess the dynamic changes in P. Accordingly, five fertilizers recovered from municipal wastewater: two struvites (STRSL and STRLQ), two ashes (ASH1 and ASH2), and iron-phosphate pelletized sludge (FeP) using triple superphosphate (TSP) as a positive control and blank (zero P) as a negative control, were applied to P poor-sand at three P doses (equivalent to 30, 60, and 90 kg P2O5 ha-1). Fertilizer impact on perennial ryegrass (Lolium perenne) dry matter (DM) and P concentration were evaluated on a monthly basis for seven months. DM and relative agronomical efficiency (RAE) have shown the same trend between the fertilizers, but only at the lowest P dose (corresponding to 30 kg P2O5 ha-1). At higher P doses (60, and 90 kg P2O5 ha-1) the differences in DM and RAE among the fertilizers diminished. STRLQ, STRSL, ASH1 and FeP expressed a rather steady P release pattern, while ASH2 had a delay of four cuts and increase afterward. Monitoring the P uptake during four months of perennial ryegrass growth turned out to be the minimum, and seven months the optimum period for reaching the full capacity of the slow-release P fertilizers.

Effect of digestate disintegration on anaerobic digestion of organic waste.

Recently, digestate disintegration gained interest as an alternative strategy to feedstock pretreatment for anaerobic digestion. This study evaluated the effect of three different digestate disintegration methods (hydrogen peroxidation, ozone treatment and ultrasound) on manure digestate, potato waste digestate and mixed organic waste digestate. Lab-scale anaerobic digestion experiments were carried out by adding disintegrated digestate to the related substrate and inoculum with simulated recycle ratios of 0.2 and 0.5. Ultrasound disintegration of potato waste digestate yields 22.5% increase in biogas production. An increase in biogas production was linked to the treated digestate amount and the treatment dosage. First order model was used to investigate the effect of digestate disintegration on the first order reaction rate constant (k). The decrease in k and increase in biogas production were linearly correlated. This correlation was explained by the increased bioavailability of the organic matter and possible negative effects of digestate disintegration on the microorganisms.