Abstract
The waste sludge from food factories has rich nutrients and useful material for fertilizer or animal feed, but quick treatments and recycling of the waste sludge are difficult due to its higher water content. We have developed a rapid composting system to make sludge fertilizer using mix of waste sludge and shredded newspaper (Sludge Fertilizer Made by Paper Mixing Method, SF-PMM). The mixture was incubated in a box reactor, continuously aerated with warm air around 35°C, and changed to mature SF-PMM, in only two weeks. To search movement of N from the SF-PMM to plants, we developed a new method to label small amounts of SF-PMM with 15N-glycine. 50 L of wastewater from a food factory was incubated with 1 L of active sludge and 3 g of 15N-glycine (98 atom% 15N), and 175 g of labeled sludge was obtained in a day. This sludge was mixed with 25 g of newspaper chips, packed between two steel meshes, and placed at 20 cm depth in the reactor composting 200 kg of unlabeled sludge-paper mixture. Composting was restarted, and after about 7 days of reaction, 15N-labeled SF-PMM 7.03 atom% 15N was obtained. The surrounding unlabeled compost contained 4.0, 4.0, and 0.8% of N, P2O5, and K2O, respectively. C/N and pH were 10 and 7.4, respectively. Komatsuna (Brassica rapa var. perviridis) was cultivated in a pot with 50 and 100 mg N of SF-PMM, and healthy plants were obtained as in the Control experiments containing 50 mg N ammonium sulfate. No growth inhibition was observed in these experiments. Even in 100 mg SF-PMM, excellent growth of the roots was observed. About 56% of the N in the plant was shown to come from 15N-SF-PMM, and about 6% of the total15N in the 15N-SF-PMM was also shown to be incorporated into the plant.
Highlights
50 L of wastewater from a food factory was incubated with 1 L of active sludge and 3 g of 15N-glycine (98 atom% 15N), and 175 g of labeled sludge was obtained in a day. is sludge was mixed with 25 g of newspaper chips, packed between two steel meshes, and placed at 20 cm depth in the reactor composting 200 kg of unlabeled sludge-paper mixture
We developed a rapid and efficient method to label the sludge in the wastewater of the food factory with 15N-glycine
A small volume of wastewater was mixed with active sludge and 15N-glycine for half a day, and the resulting active sludge was embedded into 400 L reactor tank carrying high temperature composting reaction at ∼70°C
Summary
In 2018, in Japan, 376 million tons (Mt) of industrial waste was disposed of, and in almost recent 20 years, 1996 to 2018, about 380∼430 Mt of industrial waste has been disposed of every year [1, 2]. ese industrial wastes contain around 45% of sludge containing nonorganic materials and various heavy metals, so that the reduction of the disposition of the sludge is important issue for the sustainable industries.On the other hand, in 2018, 8.8 Mt of the wastes was disposed of by the food industrial activity in Japan, along with 6.5 Mt of the waste sludge corresponding to 75% (w/w) of the total weight of the waste materials from the food industries [1]. e sludge from the food industry is generallyInternational Journal of Agronomy not contaminated with dangerous materials, such as heavy metals and chemicals. erefore, the recycle of the sludge is very important issue for the development of the food industry. Ese industrial wastes contain around 45% of sludge containing nonorganic materials and various heavy metals, so that the reduction of the disposition of the sludge is important issue for the sustainable industries. In 2018, 8.8 Mt of the wastes was disposed of by the food industrial activity in Japan, along with 6.5 Mt of the waste sludge corresponding to 75% (w/w) of the total weight of the waste materials from the food industries [1]. Erefore, the recycle of the sludge is very important issue for the development of the food industry. Waste sludge from food factories is rich in nutrition and contains organic materials and less amounts of dangerous contaminations, but the waste sludge in the food industries generally contains 80∼90% water [3]. Active sludge is used to clarify contaminated wastewater in food factories, as an eco-friendly and efficient method to treat a large volume of wastewater. Active sludge contains various microorganisms which uptake various compounds from wastewater for their growth and clarify the wastewater [4]. ese microorganisms eventually die and form sediments with the addition of coagulants (e.g., poly-aluminum)
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