Gilberto Colina

Domestic wastewater treatment using a UASB reactor

Abstract The performance of a pilot-scale (55-l) upflow sludge blanket (UASB) reactor treating municipal sewage without any supplementary heating was examined in a 200-day trial. The flow rate to the digester was kept constant, giving a hydraulic retention time of 7.6 h. Although there were some variations in the strength of the sewage, after the initial 18 days the loading rate was maintained at about 1.21 kg COD/m3 day. A pregranulated sludge was used as the inoculum, but the start-up period was still long; about 90 days. The total volatile fatty acid:alkalinity ratio was initially high, indicating an element of instability in the digester. However, as more alkalinity was added to the incoming sewage, the ratio fell below the critical value. Once this had been achieved, the digestion process stabilised and achieved a COD removal efficiency averaging 85% and a specific gas yield of 0.34 m3 methane/kg COD removed.

Acid hydrolysis and carbohydrates characterization of coffee pulp

Hydrolysis of coffee pulp with diluted sulfuric acid was studied by keeping boiling temperature with reflux, a liquid to solid ratio of 10:1 and a particle size ≤ 1.00 mm. Coffee pulp was treated using several acid concentration (C) and retention times (t). The hydrolysates were analyzed for total sugars by phenol-sulfuric acid and HPLC (TSPA and TSHPLC), reducing sugar (RS) by DNS and individual sugars by HPLC. Data were analyzed by using the Statistical Analysis System (SAS). The average sugar yields were: TSHPLC between 12.87–20.31% and 14.02–19.01%; TSPA between 23.41-19.07% and 25.74–30.58%; RS between 10.24–19.07% and 9.66–17.80% for (C) y (t) respectively, expressed as wt% of dry coffee pulp. The general range of variations for individual sugars was: xylose from 0.08 to 3.23; arabinose from 0.23 to 11.26; fructose from 0.90 to 3.00 and glucose from 1.30 to 6.31, expressed in gl−1 The sucrose varied between 0.08 and 3.96 and maltose between 0.01 and 3.50, also expressed in gl−1 of hydrolysate. The overall efficiency of hydrolysis was 64% for TSPA and 67% for RS.