農(nóng)場可降解固體廢充物高效厭氧發(fā)酵研究.pdf

1、Anaerobic digestion is an attractive option for management of farm-based biomass (animal wastes andcrop residues) because of its advantages: Better disposal of various biodegradable wastes, protection ofenvironment, Reco

2、very of materials and energy, protection of natural resources, Mitigation of Green HouseGas emissions, Reduction of waste disposal costs. Implementation of anaerobic digestion technology forhandling farm-based biomass ha

3、s been well developed in China in terms of plant numbers and nominal biogascapacity however, although China has installed much more biogas plants so far in the agricultural sector thanany other country (e.g. Germany, Swe

4、den or USA) but the practical energy generation capacity is still farbelow that of other countries with smaller number of same biogas plants. According to the visits andinvestigations within this research work as well as

5、 some other reports, a considerable number of farm-basedbiogas plants in China suffer from low biogas productivity. The major reasons associated to this problemseemed to be management and operational problems in plants (

6、e.g. digester heating, equipment maintenance,appropriate use of instruments and devices, quality of equipments, pH and nutrients control in digester, etc),low organic content in the digester feed (related to low solids c

7、ontent), incompatibility in digester design withfeedstock properties, and low organic loading rate (often associated to digester's Iumtation in acceptance ofhigh organic loads). Since in the majority of existing livesto

8、ck-based biogas plants the solid content of animal wastes isseparated and handled in other ways than anaerobic digestion and digesters work with low total solids (TS)content feedstock therefore; a part of this research w

9、as allocated to innovation of a modified plug-flow reactorfor handling of fairly high TS feedstock. A dual-compartment plug-flow reactor equipped with a passiveheating system was designed and experimentally operated by p

10、urpose of demonstrating a simple and low costtechnology for handling the biodegradable agricultural wastes. The reactor was successfully started up withpig feces as feedstock under a quasi-continuous loading and semi-dry

11、 condition with average TS content of12.8％ inside the digester and average organic loading rate of 2.06kg-VS/m3.d. The start-up phase wasfollowed by co-digestion of pig feces and pre-treated cotton stalk. Even though the

12、 digester actually worked ata temperature range 12 to 30％ below the optimal mesophilic level, acceptable rates of methane generationand VS destruction were observed. The biogas and methane yield were measured for single

13、digestion stage as0.332 and 0.202 m3/(kgadded VS) and for co-digestion stage as 0.482 and 0,325 m3/(kgadded VS)respectively. After a short delay and stabilization of hybrid plug-flow digester, a new feeding stage with pi

14、gfeces started in controlled temperature 32-35 0C in order to evaluate the performance on single digestion ofswine-based biodegradable solids. The biogas and methane production for average OLR of l.9kg_VS/m3.dwas observe

15、d as 0.450 m3/(kg-added VS) and 0.266 m3/(kg-added VS) respectively. Semi-continuous loadingof pre-treated cotton stalks to the hybrid plug-flow reactor for single anaerobic digestion demonstratedreasonable methane yield

16、 equal t0 0.184 Nm3/kg-VS although it was lower than the case of co-digestion withpig excrements but higher than upper limit of average reported methane yield of cotton stalks in the literaturethat was found equal to 0.1

17、14 Nm3/kg-VS. Another run of single digestion of pig feces was performed undermesophilic temperature and higher OLR (average 3.87 and maximum 6.05kg-VS/m3.d) that was resulted in0.273 and 0.437 m3/(kg-added VS) within 22

18、days and 37days retention time respectively. It should bementioned that the upper level of Avg. methane yield from pig manure in the literature (95％ confidence) was0.478 Nm3/(kg-added VS). Another part of this research

19、comprised the evaluation of biogas potential, methane yield andanaerobic digestion process rate of some major farm-based biodegradable solids including cotton stalks, pigfeces, rice straw and cattle excrements. Methane y

20、ields fiom cotton stalks have been reported in the range of0.022 to 0.150Nm3 per kg-VS in the preceding studies. In this study hydrothermal pre-treatment of cottonstalks was performed under atmospheric conditions (boilin

21、g in temperature up t0 100℃ for 15 minutes) priorto anaerobic digestion process through which, three agents were examined; hot water, dilute ammonia solutioncontaining 2％ NH3 (dry matter basis), and recycled liquid from

22、anaerobic process. Cotton stalks showed asignificant increase in biogas production atter mild thermal treatment in the aforementioned aqueous medium.Hot water pre-treatment resulted in 65％ increase in methane yield (110~

23、123 vs. 53~71 L/kg VSadded). Diluteammonia pre-treatment resulted in 93％ increase in methane yield (130-144 L/kg VSadded).Dilute processliquid pre-treatment concluded to the highest biogas yield over 0.450 Nm3 per kg of

24、added VS and resulted in180％ increase in methane yield (160-241 L/kg VSadded). Nevertheless, high concentration recycled processliquid had an adverse effect on biogas and methane generation resulting to decrease the biog

25、as yield asprocess liqlIid pre-treated cotton stalks produced less methane proportionally due to the degree of ammoniainhibition and low C:N ratio through which, the methane production dropped to as low as 80 L/kg VSadde

26、d at aNH4+ concentration equal t0 4900mg/kg, Energy balance evaluation far pre-treatment of cotton stalks showedsensitivity and strong dependence on TS content ofmixture in the hydro-thermal pre-treatment tank and at the

27、second rank to the methane yield therefore, the overall energy balance of the process will be positive only atTS above 10％ and methane yield above 0.175 Nm3/kg-VS upon heat recovery from pre-treatment tank. Atmospheric

28、hydrothermal pre-treatment of rice straw using recycled process liquid resulted in 94％increase in biogas production as well. Remarkable methane yield between 0.270 -0.350 Nm3/kg-added VS depending on F:M ratio and type

29、ofinoculum, however during a long retention time. Investigations showed majority of methane yield is achievedafter 30 days retention time. The same situation was observed for pig feces in wtucK Remarkable biogasand metha

30、ne yield equal to 0.519±12.4 and 0.379±9.8 Nm3/kg-added VS was obtained respectively duringthe batch tests. The greater portions of the ukimate yields are often achievable at retention times longer than30 days. Consecut

31、ive two-stage and three-stage first order equations of anaerobic digestion were examined forprediction of cumulative biogas volume over the process time. The cumulative biogas production datademonstrated a reasonable cor

32、relation (R2 0ver 0.9) and good fitness with the simplified consecutive kineticmodel. The rate of anaerobic digestion and biogas production showed a strong relationship with the ratio oforganic loading rate to the bacte

33、rial culture inside the reactor as so called "Food : Microorganisms (F/M)ratio". Hence the recirculation of partially digested contents from middle part of plug-flow reactor in order tomix with the fresh feed demonstrate