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Abstract Anaerobic digestion of organic residues (biogas technology) is one of the renewable energy technologies to produce a flammable gas as em energy source. The digested materials left pr-e serrc a good source of organic manure rich in macro and micro plant nutrients. In this investigation the evaluation of biogas and organic manures production from cow dung and sewage effluent was studied. The resulting organic manures were compared with traditional orga~ic manures, i.e. farmyard manure and poUdrette in their effect on the counts of soil microflora, the microbial enz~~tic activities, and the soil carbon and nitrogen content. Two different types of biogas digesters were chosen, the Chinese and Indian model. The digesters were fed with 200 liters of 8% and 3% total solids from cow dung and sewage water, respectively. The digestion period was 70 days. Biogas yield was mont tcr-ed daily, while its content of CH 4 and CO2 were estimated at weekly intervals. The total and volatile solids, the total nitrogen and organic carbon content were determined in initial and final stages while ammoniacal nitrogen was determined every week. When 165. the fermentation reached an elld, the residual materials were dried and crushed to be used as organic manure. Two types of soil were used, the alluvial clay loam from Moshtohor village, Kalyubia Governorate and the aandy soil from south of Jrahreer province, Behera Governorate. A four replicat19s pot experiment was conducted where the two biogas ~~d the two traditional organic manures were added to the soil at the rate of 800 kg organic matter per feddan. The soil lnoisture was adjusted at 50- 60%of w.h.c. and mentained at; this rate throughout the • experimental time. The microbial counts of bacteria, actinomycetes, fungi, aerobic and anaerobic celLu Lose decomposers, coliform group and Shigella~. and Salmonella~. were estima: ted at the periods of 0, 15:t 30, 60, 90, 120 and 160 days. Also the soil total nitrogen and organic carbon content were determined at the aformentioned periods. The microbial acti vi tiE~S represented by dehydrogenase, phosphatase, urease and nitrogenase were measured at the periods of 0, 1, 3, 5, 7, 15, 30, 60, 90, 120 and 160 days. 166. The obtained results can be summar-i.zedas follows:- 1) The sewage sludge started biogas production from the first day in both types of d.igesters while cow dung started after 14 and 18 daysin Chinese and Indian tJ~es, respectively. The daily biogas production increased till 16 and 30 days for sewage sludge and cow dung, respectively then decreased thereafter. The cumulative gas production was higher in Chinese than Indian type for both residual materials. In Chinese type cow dung produced more gas than sewage sludge ~mile in the Indian type sewage sludge produced more gas than cow dung. 2) The methane content of the gas produced from the Indian was similar to that produced from the Chinese digester when using the same organic materials. But the gas produced from the sewage sludge digestion contained apparently higher percentage of methane than that produced from cow dung. 3) The losses in vol~~ile or total solids as a result of the sewage sludge fermentation were higher than cow dung. The losses of either residue in the two digesters were very close to each other. 4) It was found that the total nitrogen content of the digested materials was lower at the end of digestion than the respective value in the initial sample. The loss was higher in Chines(~ than Indian digesters and in sewage sludge than cow d~~. The ammoniacal nitrogen reached its maximum. concentration in the period 7-28 days according to the type of digester an<i the ~ of residue, then gradually decreased thereafter. 5) It can be concluded that the Chinese type of digesters was more efficient in the anaerobic digestion of organic residues, since it produced almost the same quanti ty of organic manure as the Indian type while it produced more amounts of bf.ogas than the Indian digester. 6) The application of organic manures to the alluvial and sandy soils Lncr-eased the total counts of bacteria and actinomycetes. The digested cow dung was more effective followed by the digested sewc~e sludge > farmyard manure > poudrette, except in the case of sandy soil, the actinamycetes count was more in poudrette than farmyard manure. Also it was clear that the ef”fect of manuring the sandy soil in increasing the counts was more apparent than alluvial soil. 7) The total count of fungi was enhanced by the application of organic manures, digested biogas manures was more effective than traditional organic manures in enhancing the funGal growth. Digested sewage slUdge gave a peak, higher than cow dung followed by poudrette then the farmyard manure. 8) The counts of aerobic cellulose decomposers were apparently stimulated iDy the addition of digested cow dung followed by digest13d sewage sludge then the farmyard manure and poudrette. In case of the sandy soil the two digested organic manures showed nearly the same level of activation followed by farmyard manure which is more effective than poudrette. 9) As was expected the digested organic manures showed higher densities of cmaerobic cellUlose decomposers than traditional organic marlures and control due to the anaerobic conditions in the ferment or • In alluvial soil the digested cow dung was mor-e effective than digested sewage sludge followed by farmyard manure and poudrette, while in the sandy soil the order was digested sewage sludge > digested cow dung ’> poud.rette > FYK. , . 10) The poudr-etbe and liisested sewage sludge showed higher increase in cOQnts of coliform group than farmyard manure and poudrette in both alluvial and sandy soils. This was attributed to the origin of both poudrette and digested sewage sludge which the human excretes. The COUIl,ts of coliform group decreased gradually from the 60th d~ till they completely disappeared. 11) There was not any Golony of,Salmonella.!!l2.- and Shigella .£ll2,. in the platE~s of control or soils treated by biogas manures, while in soils treated by tradi tional manures there we:re some colonies at the beginning and then disappeared rapidly. 12) The dehydrogenase activity was increased in the sandy and alluvial soil treated with organic manures than control and this was attributed to the growth and proliferation of soil microorganisms following the moistening of the soil. Dehydrogenase activity slightly increased for few days, then graduallJ’ decreased thereafter: The digested cow dung showed thE! highest activity followed by farmyard manure, poudrette, while the sewage sludge showed the lowest figures. 13’) The addition of organic ::..anuresfavoured the phosphatase activity in a manner related to the COUll ts of different microbial .i;roups. In alluvial soil the results showed the superiority of the sewage sludge followed by digested cow dung > farmyard manure> poudrette. Phosphatase enzyme in sandy soil showed lower activity than alluvial soil. The order of stimulation in sandy soil is as follows: digested cow dung > farmyard manure :> digested sewage sludge > poudrette. 14) The most efficient organic manure in enhancing the proliferation of urea hyc~olyzing microorganisms, and urease actiVity, as a result, was the digested cow dung followed by sewage sludge. It was suggested that the presence of considerable concentration of heavy metals in sewage sludge may act in the inhibition of urease activi ty. The least stimulation was observed in farmyard manure followed by poudrette. This was true for both sandy and allUvial soils. 15) The application of organic. manures to the soils increased the efficiency of ni.trogen fixation as expressed by the nitrogenase activity. Di5ested cow dung showed highest figures allover the experiment followed by f’arm- yard mEL~ure then diGested sewage sludge, while poudrette showed the least activity. Xitrogenase activitjin sandy soil was apparently less stimulated than alluvial. In sandy soil the digested cow dung favoured nitrogenase activity more than digested sewage sludge followed by farmyard manure and poudrette. 16) The addition of the organic manures increased the organic matter content of the soil. The increase was almost the same in all the tested manures. A gradual decrease in organic matter was observed till the end of the • experimental period. A positive ~elation between the rapid decomposition of the organic matter and microbial activity can be demonstrated in the same period. The same trend was observed inalluvia.l and sandy soils. 17) The initial samp’l.ee of manured sandy and alluvial soils contained higher amountis of total nitrogen. This total nitrogen content decreased early and then gradually increased thereafter till the end of the experimental period. The digested cow dung treatment showed the highest level of total nitrogen allover the experimental period, while thtl’ othuthree manures exhibited many close levels which were much less than the forIuer. 18) The C:N ratio of both soils was not affected by the incorporation of organic manures. However, the ratio was gradually narrowed till the end of the experiment. 1.9) Manuring the testEld sod.Ls increased their content of the ammoniacal nitrogen, but it was rapidly assimilated by soil microorgcwism and decreased after 15 days of manuring, then a gr-adua’l, decrease for 90 days followed by a slight build U]~. The four applied manures showed the same level of NH4··-Nalmost a’Tlover’ the experimental period. 1.0) The nitrate nitrogen content in alluvial soil showed reverse trend to that of NH4-:n. The maximum stimulation of nitrifiers was observed in the digested sewage sludge treatment followed by digested cow dung then poudrette and farmyard manure, respectively. The same trend IN’a 5 observed in sandy soil, but the initial samples showed equal amounts of nitrate nitrogen in control and manured soil. |