Sewage phosphorus recovery through sachets loaded with water treatment plant sludge.

Conventional wastewater treatment plants (WWTPs) present low phosphorus (P) removal capacity. Conversely, water treatment plants (WTPs) produce sludge with great P sorption from wastewater; however, directly adding the sludge into the wastewater treatment system could increase the effluent turbidity. As a novel approach, the present study evaluated the performance of WTP sludge within paper sachets for P removal from treated sewage. Different sludge concentrations (2-30 g L-1) and contact times (1-27 d) were applied to treat sewage from a university WWTP outlet. The sludge was characterized by P, Fe, and Al content. Larger sludge masses showed higher P removal efficiencies due to their high Fe content, especially at longer contact times (up to 100% at the final of the experiment). However, there is a more significant P reduction in the first 10 d (more than 90% in the most efficient treatment - 30 mg L-1). Based on the kinetic and isotherm analyses and the sludge chemical composition, precipitation proved to be a mechanism of great importance in P removal. Therefore, WTP sludge sachets can be a promising way to remove P from sewage, and the formed solid waste might be reused as an alternative fertilizer.

Hydrothermally-altered feldspar as an environmentally-friendly technology to promote heavy metals immobilization: Batch studies and application in smelting-affected soils.

Hydrothermally-altered feldspar (HydroPotash, HYP) possesses, among other physicochemical properties, high pH buffering and cation exchange capacity. Therefore, it may potentially remove heavy metals from aqueous solutions and immobilize these metals in contaminated soil. This study aimed to evaluate the capabilities of two types of HydroPotash (HYP-1 and HYP-2) and a zeolite sample (a commercial adsorbent) for immobilizing cadmium (Cd), zinc (Zn), and lead (Pb) from both aqueous solution and contaminated soils from a Zn-smelting area (classified as soilhigh, soilintermediate, and soillow based on their level of soluble metal concentration). Sorption studies in natural suspension pH showed that HYPs removed 63.8-99.9% Zn, 20.6-40.7% Cd, and 68.4-99.7% Pb from aqueous solution. In the batch test with controlled pH (at pH 5.5), HYPs sorbed more Cd than zeolite. Analyses of scanning electron microscopy-energy dispersive X-ray spectroscopy after desorption showed the presence of Pb at HYP-2, indicating that this metal was effectively adsorbed. In soilhigh HYPs immobilized 99.9% of Zn, Cd, and Pb after one week of soil incubation with these products. The HYPs immobilization effect persisted up to 84 days of soil incubation with these products. The increased soil pH promoted by HYPs appears to be the main factor controlling metal sorption. In conclusion, HydroPotash can be used as an adsorbent/amendment to effectively immobilize heavy metals in both water and contaminated soils by precipitation and adsorption. Our findings indicate the high potential of this material for Cd, Zn, and Pb stabilization, which is of great relevance when recovering areas affected by mining/smelting activities with multi-element contamination.

Long-term effect of biochar-based fertilizers application in tropical soil: Agronomic efficiency and phosphorus availability.

Incorporation of phosphorus (P) into an organic matrix may be an effective strategy to increase plant P use efficiency in high P-fixing soils. The objective of this work was to evaluate the effect of biochar-based fertilizers (BBFs), produced from poultry litter (PLB) and coffee husk (CHB) enriched with phosphoric acid and magnesium oxide, in combination with triple superphosphate (TSP) on plant growth and soil P transformations. Treatments were prepared as: TSP, CHB, PLB, CHB + TSP [1:1], CHB + TSP [3:1], PLB + TSP [1:1] and PLB + TSP [3:1]; with numbers in brackets representing the proportion of BBF and TSP on a weight basis. Cultivations were: Mombasa grass, maize, and common bean interspersed with fallow periods. After cultivations, a sequential extraction procedure was employed to determine P distribution among different P pools. A kinetic study was performed and revealed that TSP released approximately 90% of total P, and BBFs less than 10% in the first hour. BBF alone or in combination with TSP presented higher or similar biomass yields, relative agronomic effectiveness, and P uptake when compared with TSP. As for the soil, BBFs increased non-labile P fractions, which can be due to pyrophosphate formed during pyrolysis. According to these results, BBFs could totally or partially replace conventional soluble P fertilizers without compromising crop yield either in the short and long-term.

Fast and effective arsenic removal from aqueous solutions by a novel low-cost eggshell byproduct.

Developing alternative green solutions for local and correct recycling of eggshells waste (ES) are needed by the egg-processing industries. In this study, we proposed transforming ES into a novel low-cost chemical compound named hydroxyl-eggshell (ES-OH) and investigated its capacity for arsenic (As) removal from aqueous solutions. Laboratory experiments were conducted to investigate the effects of ES-OH doses, pH, kinetics, and isotherms on As removal efficiency. The kinetics study showed that ES-OH removed nearly all As from solution in less than 15 min. The pseudo-second-order model described the process, and the maximum As removal capacity predicted by the Langmuir isotherm model was 529 mg g-1. Using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy with energy dispersive X-ray detector (SEM-EDS), and X-ray diffraction (XRD), we found that the As removal mechanism by ES-OH was due to vladimirite precipitation, followed by weak electrostatic interactions between the precipitate and arsenate ions. Finally, after an economic analysis, we conclude that besides being a novel and economical income source, egg-producing companies might implement the ES-OH production process as a local environmentally-friendly way of recycling eggshells and reducing water As contamination.