Anaerobic digestion as a core technology in sustainable management of organic matter.

In the past decades, anaerobic digestion (AD) has steadily gained importance. However, the technology is not regarded as a top priority in science policy and in industrial development at present. In order for AD to further develop, it is crucial that AD profits from the current fuel issues emerging in the international arena. AD can provide low-cost treatment of sewage and solid domestic wastes, which represents a vast application potential that should be promoted in the developing world. Furthermore, the developments in the last decades in the domain of anaerobic microbiology and technology have generated some interesting niches for the application of AD, such as anaerobic nitrogen removal and the treatment of chlorinated organics. Recently, AD has also generated some serendipities, such as the use of AD in processes for sulphur and calcium removal and the coupling of AD with microbial fuel cells. The international developments in terms of bio-refineries and CO2-emission abatement are of crucial importance with respect to the impetus that AD will receive in the coming decade. There should be little doubt that by placing the focus of AD on the production of green energy and clean nutrients, the future of AD will be assured.

Removal of ammonium nitrogen from pretreated domestic sewage using a natural ion exchanger.

Ammonium nitrogen was removed from pretreated domestic sewage using a natural zeolite-clinoptilolite, applying a column with downflow regime. The pretreated wastewater had an average total ammonium nitrogen (TAN) of 23 mg l(-1). Ion exchange was allowed to take place under normal sewage treatment plant conditions and tropical temperature setting. The sorption capacity of the natural clinoptilolite was studied with the column fitted to a chemically enhanced primary treatment (CEPT)-upflow anaerobic sludge blanket (UASB) system, operating at 33 degrees C. Optimal operational cation exchange capacity (CEC) of 14 g TAN kg(-1) zeolite was obtained for the zeolite granulometry of 1-2.5 mm in a reversible way. The treatment was done at 3.9 bed volumes (BV) per day, and breakthrough was attained after about 560 BV. Regeneration of exhausted zeolite was effected with a 25 g NaCl l(-1) salt solution, rendering the column amenable to reuse. Employing a 3-column test and bed contact times of 6, 2.6 and 1.1 minutes, the use of pretreated wastewater with average concentration of 38 mg NH4(+)-N l(-1) showed that the operational cation exchange capacity also depended on flow rate, with the removal efficiency decreasing from 95 to 47% with increase in the flow rate. Overall, the approach of removing TAN from digested sewage offers potential to recover the TAN from the domestic wastewater, thus minimizing the need for subsequent nitrification-denitrification of the whole water volume.

Stimulation of methanogenesis in a laboratory scale UASB reactor treating domestic sewage by Fe(0) application.

The effects of application of zero valence Fe (Fe(0)) on the anaerobic digestion of sewage was investigated using two laboratory scale UASB reactors. One reactor had Fe(0) addition in a container found midway along the recycling loop. The other one was a control reactor. In a test run period of 76 days, the Fe(0) application significantly increased the CH, yield by 8.7% and decreased the effluent COD concentration by 21.0% relative to the control reactor. A decrease of the H, concentration of biogas and the CODs/CODt ratio in effluent by Fe(0) application were observed. The obtained results imply that the methanogenesis and COD removal efficiency of the UASB reactor were stimulated by Fe(0) application. The higher performance of the reactor with Fe(0) application arises from the integrated functions of Fe(0) or its ionic state as donor of H2, macronutrient, and flocculant. This study showed that the supply of Fe(0) to a UASB can improve the methanogenesis and the overall COD removal of a UASB reactor treating low-strength domestic waste water.

Development of a sustainable treatment technology for domestic sewage.

We propose an integrated chemical-physical-biological treatment concept for the low-cost treatment of domestic wastewater. Domestic wastewater was subjected to a chemically enhanced primary sedimentation (CEPS), followed by treatment in an upflow anaerobic sludge blanket (UASB) reactor. In addition, a regenerable zeolite was used to remove NH4+, either after CEPS pretreatment or after biological treatment in the UASB reactor. The CEPS pretreatment consisted of the addition of a coagulant (FeCl3) and an anionic organic flocculant and removed on average 73% of the total chemical oxygen demand (CODt), 85% of the total suspended solids, and 80% of PO4(3-) present in the wastewater. The UASB system, which consequently received a low CODt input of approximately 140 mg/L, was operated using a volumetric loading rate of 0.4 g CODt/L.d (hydraulic retention time [HRT] = 10 h) and 0.7 g CODt/L.d (HRT = 5 h). For these conditions, the system removed about 55% of the CODt in its influent, thus producing an effluent with a low CODt of approximately 50 mg/L. The zeolite, when applied in batch mode before the UASB reactor, removed approximately 45% of the NH4+, whereas its application as a post-treatment cartridge resulted in almost 100% NH4+ removal. The simple design and relatively low operating costs, due to low costs of added chemicals and low energy input (estimated at Euro 0.07-0.1 per m3 wastewater treated), combined with excellent treatment performance, suggest that this system can be used as a novel domestic wastewater treatment system for developing countries. Therefore, the system is called a Low-cost, Integrated Sewage Treatment (LIST) system.