Wastewater
Domestic wastewater has a potential CH4 production/emission of c. 14m3 per person per year. The collection, transport and treatment strategy that is applied will determine to what extent CH4 can be recovered and used for energy production, whether CH4 will be partially emitted, and if CO2 instead of CH4 will be produced. Controlled anaerobic treatment is a challenging but potentially important technology for reducing energy use and increasing energy production, while reducing CO2-eq emissions (Aiyuk et al, 2006).
Anaerobic treatment of domestic sewage is commonly applied intropical latitudes, while at higher latitudes it is used more rarely. Lownutrient removalefficiencies and high dissolved CH4 concentrations are two disadvantages of low-temperature anaerobic treatment. Newly developed nutrient removal techniques, such asanammoxand denitrification with CH4 (Strous and Jetten, 2004) may enable future application of low-temperature domestic sewage treatment. Recently, it was shown that the direct anaerobicoxidation of CH4coupled to denitrification of nitrate is possible (Raghoebarsing et al, 2006). Future application of this microbial conversion process could solve two problems in one, viz. removing high dissolved CH4 and nitrogen contents in low-temperature effluent of anaerobic treatment systems for domestic sewage.
Another possibility is the separation of domestic waste(water) streams at the source, with subsequent community-based on-site anaerobic treatment of the concentrated black water andkitchen wasteat an elevated temperature for the production of energy (grey water is separately treated). Successful demonstrations have already been made in Germany and The Netherlands (Otterpohl et al, 1999; Zeeman et al, 2008). Worldwide, domestic on-siteseptic tanksare frequently applied for domestic sewage treatment, especially in rural areas. The CH4 that is produced is generally not recovered or used as an energy source. A greater number of septic tank systems could be improved and operated as UASB-septic tanks for increased efficiency and biogas production (Lettinga et al, 1993). Indeed, by feeding black water and kitchen waste to a UASB-septic tank, ~60 per cent of the energy for cooking can be provided by the produced biogas (Zeeman and Kujawa, unpublished results).
High-rate anaerobic treatment for industrial wastewater was first applied on a commercial scale in the sugar industry in the mid-1970s in The
Netherlands. Since that time the technology has developed into a standard method of wastewater treatment for a wide variety of industries (Frankin, 2001). For industrial wastewater, the application of anammox and other nutrient removal processes may further improve the efficiency of wastewater treatment processes. In addition to producing energy by application of anaerobic treatment, many industries are becoming interested in closing water and resource cycles. Rearranging the conventionally appliedwater cyclesin industries offers many more advantages than solely 'increasing' thewater resources。荷兰的主要驱动产业优化water use are related to (van Lier and Zeeman, 2007):
• optimized usage of raw materials (less wastage);
• optimizedl雷竞技 ; as heating surface water and groundwater to production temperatures requires ~4.2MJ °C-1 m-3, a substantial energy benefit can be gained if treated process water is reused in the production process;
• reduced costs related to water intake taxes and costs fordrinking water/industrial water;
• reduced costs for wastewater conveyance and treatment.
This chapter has discussed many different issues regarding the emission of CH4 from wastewater and manure. It is clear that different measures can be taken to either promote controlled CH4 production or mitigate undesired CH4 emissions. The recovery of CH4 is important both from an energetic standpoint and from the perspective of greenhouse gas emissions. Therefore it is important that any CH4 emitted is at least flared, but preferably used for energy generation. Finally, a matter of immediate concern is the fact that treatment of both industrial and urban wastewater is still comparatively rare in developing countries: for example Asia at around 35 per cent and Latin America at about 14 per cent (WHO/UNICEF, 2000). As such, already-scarce water resources for many millions of people are even more threatened (van Lier and Zeeman, 2007).
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