This study investigated the effects of pH, temperature and hydraulic retention time (HRT) and organic loading rate (OLR) on hydrogen production from dairy processing waste (DPW) in semicontinuous 60 L pilot induced bed reactors (IBR). Results show pH played a key role on hydrogen production and the optimal pH range was in 4.8-5.5. Digestion under thermophilic temperatures (60 °C) had advantages of gaining higher hydrogen yield and suppressing the growth of methanogens. The optimal OLR was 32.9 g-COD/l-d at HRT of 3 days. Under optimal conditions highest hydrogen yield was 160.7 ml/g-COD removed with 44.6% COD removal. Two-stage digestions demonstrated more energy gain from methane production and further COD removal. The overall gas production in two-stage digestion was 71.7 ml hydrogen and 61.0 ml methane per gram DPW COD. The overall COD removal under optimal conditions was 88.2%.

Anaerobic Digestion Model Number1 (ADM1) was modified in order to predict accurately the impact of co-digesting bakery waste (BW) with municipal sludge (MS). BW is an industrial waste (300,000 gallons per day in USA) that contains a high concentration of organic matter (carbohydrates, low lipids and non-detected proteins). BW is an easily biodegradable substrate for creating a favorable microorganism growth environment, which enhances the biogas production needed for wastewater facilities. The modified ADM1 successfully predicted changes in pH, volatile fatty acids (VFA), propionic acid and methane gas production. The ADM1 outputs were compared to experimental batch reactor results of actual BW addition percentages in order to validate the model. Stability of the digestion process was achieved until the ratio range of 37-40% BW: 60-63% MS, and the digestion processes were inhibited at higher ratios of BW. This research provides an alternative to BW management through utilizing the BW to enhance methane production.

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