Anmol Parajuli
anmolparajuli7@gmail.com

PLAN:- INTRODUCTION 

The mini-project is about the dark fermentation of carbohydrate enriched  food waste. Dark fermentation is the fermentative conversion of organic  substrate to bio-Hydrogen involving series of biochemical reactions similar  to anaerobic digestion. In microorganisms, fermentation is the primary  means of producing adenosine triphosphate (ATP) by the degradation of  organic nutrients anaerobically. The byproducts that are produced through  dark fermentation processes are organic acids and Carbon dioxide. Hydrogen can be stored and purified through large scale bio-fermentation  plants through dark fermentation and this mini-project aims to check its  validity whether the Hydrogen supply can be continuous with the  continuous supply of food waste in the setup. This process can serve us in  many ways. The areas with benefits are energy generation, waste  management, agricultural productivity through the production of fertilizers  by treating the digestate and soil amendment.  

The Hydrogen production yield and the reaction: 

4 mol Hydrogen + 2 mol Acetate per mol of glucose. 

C₆H₁₂O₆ + 2H₂O 🡪 2CH₃COOH + 2CO₂ +4H₂ 

DESIGN:- METHOD 

Food Waste Composition: 

The actual food waste was risky to be used during COVID19 and food  waste constitution is very sensitive when it comes to production of  Hydrogen through fermentation. The composition of the standard food  waste was accessed through research based on the Asian food waste  composition from a journal article. The composition is given in the table: 

Parameters to be considered: 

1. TS/VS: Total Solids and Volatile Solids was determined through  standard methods(APHA, 2005). The TS and VS of the food  substrate were found to be 15.93% and 14.47% respectively. The  inoculum’s TS and VS were found to be 0.29% and 0.05%. 

2. S:I ratio: The substrate used is food waste and the inoculum is  anaerobic digestate. The food and inoculum is supplied to the reactor  in the ratio 1 in terms of VS. 

3. OLR: The substrate and inoculum ratio are fed to the reactor in  terms of OLR. The organic loading rate is an important parameter  because it indicates the amount of volatile solids to be fed into the  digester each day. The OLR of 0.5 g VS/L day is fed for the demo. 

4. HRT: The Hydraulic retention time (HRT) is a measure of the  average length of time that a soluable compound remains in a  constructed bioreactor. The HRT of 20 days is maintained and  volume is studied for a week, and the volume of gas is measured for  a week. 

Materials Required 

3 air tight Bottles 
black cloth 
4 IV sets, 
Hot glue gun 
Stirrer 
Binder clips 
10% NaOH solution

DEVELOP:- Setup: 

I have modified the pre-existing setup focusing on the production of  bio-Hydrogen by dark fermentation process, by keeping the reactor  system wrapped with black cloth so that light doesn’t pass inside it. 

The setup worked in mesophilic temperature conditions because  mesophilic ranges from 20-40 degree Celcius. The apparatus  consists of : 

1. Reactor for the feeding with IV pipes to supply the feed  everyday and to let the gas flow out of it. 

2. Buffer for safety because the liquid might leak through IV  pipes in worst cases. 

3. NaOH solution chamber( Water displacement chamber) to scrub CO₂ present in the gas, for specifying Hydrogen  production. The chamber is kept upside down while letting  the gas flow through it so that the water displaced is  collected and measured while the gas passes through the  chamber and remains in the chamber. The IV pipe can be  turned on to store tha gas in balloon. The gas displaced is  measured in ml.

Results: 

The volume of gas released per day is measured through water  displacement process, and the amount of gas released is checked on  a daily basis throughout the week. The daily data throughout the  week is tabulated in ml. The gases yield in a week (after for days of  unstable process) is found to be 44, 21.5, 34, 53, 38, 38, 45 ml per  day throughout the week with the food weight of just 1.38g per  day. The feed was supplied at an OLR of 0.5 gVS/ L day. The food  weight might sound too less but it is most suited to supply the food  in the S:I ratio of 1 in terms of VS. As the inoculum has very less  VS% , the food waste could be supplied in very little amount in the  reactor which had the volume of 0.5 L. 

Few days, the setup couldn’t work well because of the growing  phase of the bacteria after which the yield averaging 39.1 ml was  observed with just 1.38 g of feeding per day. This projects to the  yield of 28.333 L of bio Hydrogen with 1 kg of feed without the  access to fermentative reactors.