Explain the mode of operation of the 2 bioreactors in Figure 16.12; Agitated (mixed) in vessel composting bioreactors (A) circular; (B) rectangular.
In mechanically agitated in-vessel composting, organic waste is converted to compost in enclosed containers where the temperature and oxygen level are closely monitored (Google Books, 2018).
Bioreactor (A) circular is also known as the mixed (dynamic) vertical reactor.
This system of composting involves a combination of forced aeration and the use of a cylindrical tank. The tank comprises of augers; drilling devices which consist of rotating helical screw blades. These augers are supported by a bridge attached to a central pivoting structure. The bridge equipped with a set of hollow augers is rotated slowly. As the arm rotates, the augers are turned (Frank and George, 2018).
The material to be composed (the wastewater solids and the bulking agent) is fed in at the top of the bioreactor on either a continuous or batch basis and is agitated to facilitate oxygenation. The mixture is mixed or periodically agitated by using mechanical device during the processing. The composted material is removed at the bottom of the reactor (MARK and RONALD, 2018).
Air is forced from the bottom of the reactor into the composting mix. The retention time varies. The discharged material needs to be windrowed until stability is reached if the retention time is less than three weeks (Frank and George, 2018).
Bioreactor (B) rectangular also known as the mixed (dynamic) horizontal reactor or the open, horizontal, rectangular tank comprises of conveyors. The extraction conveyor either mixes the compost in the reactor or discharges the compost to the outfeed conveyor (Fotedar, 2018).
This system of composting involves a combination of forced aeration and tumbling. Bioreactor B involves the use of a long horizontal bin where properly prepared waste is fed in. Tumbling is conducted by the use of a traveling endless belt. Air is forced through the perforated plates present at the bottom of the bin into the composting mix. The belt is passed through the composting mix periodically (Frank and George, 2018).
The composting materials are primarily processed ‘in vessel’ for one to two weeks prior to further composting and curing in windrows or static piles. Once the compost comes out of the vessel, it requires a few weeks or even months for the microbial activity to stabilize and the pile to cool (Frank and George, 2018).
This type of composting is appropriate for sewage sludge, mixtures of MSW and properly bulked high- moisture food wastes. It takes around one to two months (time involved in ‘in-vessel’ and windrow) for an in vessel composting to be completed (Frank and George, 2018).
The daily operation of the agitator/mixer moves the material down the length of the reactor, which makes space available to load new material in the reactor each day (Fotedar, 2018).
In vessel composting has a greater potential to produce high quality compost and very uniform compost. The system minimizes odour and shorten the composting period by controlling air flow, temperature and oxygen concentration. (Extension.uga.edu, 2018)
In vessel composting is preferred over other methods of composting as the process is not affected by the weather, less spaces is required and less workforce is required. Some of the drawbacks of such system of composting are that this type of compositing is costly, requires careful management and the system is sensitive to changes in characteristics of bio solids and bulking agent. (MARK and RONALD, 2018)
In vessel composting is designed to speed up the decomposition process of organic materials. (MARK and RONALD, 2018)
Extension.uga.edu. (2018). Food Waste Composting: Institutional and Industrial Application | UGA Cooperative Extension. online Available at: http://extension.uga.edu/publications/detail.html?number=B1189&title=Food%20Waste%20Composting:%20Institutional%20and%20Industrial%20Application Accessed 17 Oct. 2018.
Fotedar, A. (2018). Composting – A Solution to the Burning Problem of Solid Waste Management – The Permaculture Research Institute. online The Permaculture Research Institute. Available at: https://permaculturenews.org/2017/06/23/composting-solution-burning-problem-solid-waste-management/ Accessed 17 Oct. 2018.
Google Books. (2018). Handbook of Environment & Waste Management. online Available at: https://books.google.mu/books?id=_ZG6CgAAQBAJ&pg=PA81&lpg=PA81&dq=mixed+(dynamic)horizontal+reactor+for+composting&source=bl&ots=E7PPRe2owI&sig=pyFI2y3-aKiDt3ZLe4ki8UeHCcc&hl=en&sa=X&ved=2ahUKEwjQr_O0uIveAhXDEywKHaLxCpgQ6AEwDHoECAgQAQ#v=onepage&q=mixed%20(dynamic)horizontal%20reactor%20for%20composting&f=false Accessed 17 Oct. 2018.
Frank, K. and George, T. (2018). Handbook of Solid Waste Management. online Sanitarac.pro. Available at: https://sanitarac.pro/wp-content/uploads/2017/07/Solid-Waste-Management.pdf Accessed 18 Oct. 2018.
MARK, E. and RONALD, A. (2018). Evaluation of Composting Feasibility for Regional Implementation. online Pdfs.semanticscholar.org. Available at: https://pdfs.semanticscholar.org/dc82/85736542cffd971ce7ba30418844249690fd.pdf Accessed 17 Oct. 2018.
Dkmm.org. (2018). Types of Composting. online Available at: https://www.dkmm.org/types-of-composting Accessed 17 Oct. 2018.