Waste management: a study on generating organic fertilizer from oil and grease trap systems

The grease and oil trap systems (GOTS) of four university food service establishments (FSE) were assessed and treated to evaluate the potential use of the sludge collected to produce compost. The sludge collected from each FSE was kept in a drying bed for 30 days (SDB), during which time calcium oxide was frequently added for stabilization. The sludge deposited monthly was reduced to half after the drying process and was then deposited in a composter and mixed for a period of 22 days with constant agitation. The compost obtained was treated with degrading enzymes and was denominated enzymatic composting (EC), while the remaining compost was not treated with enzyme and was denominated non-enzymatic compost (NEC). The total composting cycle of the sludge lasted 83 days, during which time various physical and chemical analyzes were conducted in the three types of substrates (SDB, NEC, and EC). The total time of the research was 2.5 years. The percentages of phosphorus, potassium, magnesium, and calcium suggest the use of the three substrates as organic fertilizer. A recommendation resulting from this research is to evaluate the sludge quality by mixing it with other substrates such as fruit peels with high nitrogen content and the sludge from wastewater treatment systems.

Process-adapted temperature application within a two-stage rivet forming process for high nitrogen steel

Mechanical joining technologies like self-piercing riveting are gaining importance with regard to environmental protection, as they enable multi-material design and lightweight construction. A new approach is the use of high nitrogen steel as rivet material, which allows to omit the usually necessary heat treatment and coating and thus leads to a shortening of the process chain. Due to the high strain hardening, however, high tool loads must be expected. Thus, appropriate forming strategies are needed. Within this contribution, the influence of applying different temperatures for each forming stage in a two-stage rivet forming process using the high nitrogen steel 1.3815 is investigated. The findings provide a basic understanding of the influence of the temperature management when forming high nitrogen steel. For this purpose, the rivets are not formed at the same temperature in each stage, but an elevated temperature is applied selectively. Different process routes are investigated. First, cups are manufactured in stage 1 at room temperature, followed by stage 2 at 200°C. Second, cups are formed in stage 1 at 200°C and used for stage 2 at room temperature. By comparing the findings with results when applying the same temperature in both stages, it is shown that the temperature during the first forming operation has an effect on the forming behaviour during the second forming stage. The required forming forces and the resulting rivet hardness can be influenced by process-adapted temperature application. Furthermore, the causes for the temperature impact on the residual cup thickness in stage 1 are evaluated by a cause and effect analysis, which provides a deeper process understanding. The thermal expansion of the tool and the billet as well as the improved forming behaviour at 200°C are identified as the main influencing causes on the achieved residual cup thickness.

Remedy for Collapse of ZIF Derived Carbon: Micro-Pore Filled Synthesis to Improve ORR Catalytic Property

Zeolitic imidazolate framework (ZIF) derived carbons deliver outstanding performance as oxygen reduction reaction (ORR) catalysts. However, their electrocatalytic activities are limited due to unavoidable collapse of ZIFs upon pyrolysis, which results in degradation of porosity, sintering of metals and loss of active sites. In this work, a micro-pore filling strategy was employed to strength the architecture of ZIF by using size matched cyanamide molecules as fillers. The cyanamide with high nitrogen content shows a triple effect in stabilizing the carbonaceous skeleton, preserving of metal containing active sites and improving the conductivity of matrix. Therefore, the as-prepared Fe, Co co-doped ZIF derived carbon (FeCo@NC-N) delivers a significantly improved electrochemical activity for ORR than its unfilled counterpart, with half-wave potential upshifted by 30 mV (0.84 V vs. RHE). Besides, a promoted power density of home-assembled zinc-air battery is obtained when FeCo@NC-N is applied as cathode catalyst. This work demonstrates a reliable approach to mitigate framework collapse of metal organic framework (MOF), thus may open a new way for fabrication of MOF based catalysts with increased loading of pores and active sites.