Complex Ecological Bed Systems Is Applied Research In The Agricultural Non-point Source Pollution Control

Fuxian Lake, the second deepwater one in China, has shown a speeding nutrition-rich tendency in recent years, whose resulting factors include the increasing external pollution, the severe destruction in the lakeside zone, the quick accumulation of nutritive salts (such as N, P) in the lake and the simplicity & the weakness of the lake's ecological system, etc. It has been found that the basic cause for the speeding nutrition-rich tendency lies in the non-point source pollutions within the lake's runoff field (including the high-intensity cultivation, the mass-use of fertilizers pesticides, rural sewage & rubbish, etc.) which have been input into Fuxian Lake through some rivers, so the anti-pollution against these rivers is the key of protecting the lake.The main pollution source of Fuxian Lake is the northern bank whose severest pollution canal is Yaonigou-Nongguanzhonggou, which gathers all the non-point source wastewaters from twenty villages & small towns and more than 4700 mu farmlands in the runoff field. Therefore, the anti-pollution against Yaonigou-Nongguanzhonggou becomes the key to control the non-point source pollution in the northern part of Fuxian Lake. There is a distance of 50 meters between Yaonigou and Nongguanzhonggou. A 22.5-mu deserted lake beach in west of Nongguanzhonggou should be treated and then we could establish a non-point source wastewaters constructed wetland system which consists of Nongguanzhonggou, an overflow weir in Yaonigou, a solid rubbish salvaging platform, a waste boom, a precipitating adjustment tank, oxidation ponds, a subsurface flow artificial wetland and a free water system artificial wetland. Designed with a treatment scope of 4400 m3/day, the hydraulic retention time of 518 hours, this system could have a wastewater treatment capability of 1.6 million each year which counts for 36.2% of the total wastewater in Yaonigou.The results of our test research showed that this system could remove all kinds of 750-ton rubbish in the canals by means of salvaging each year. On the design condition of a high hydraulic load (44cm/d), 61.8% of SS, 3.6% of TN, 5.9% of TP and 8.5% of NH3-N could be removed through the precipitating adjustment tank; 20%-90.32% of SS, 34.55% -57.60% of CODcr, -4.12%-42.53% of TN, -28.75%-61.44% of NH3-N and -11.71%-35.77% of TP could be removed, but there exists a secondary pollution phenomenon through the oxidation ponds; 9.10%-29.61% of CODcr, 5.60%-33.71% of TN, 2.41%-27.44% of NH3-N and 11.19%-60.00% of TP could be removed through the subsurface flow artificial wetland and for differentsubsurface flow wetland structure, different N and P could be removed, TN has an average removing capability order of slag plus reed(30.17%) > big pebbles plus umbel bamboo plus cattail (25.94%) > pebbles plus reed (19.11%) > centimeter stones + cattail (18.22%) and TP has the order of pebbles plus umbel bamboo plus cattail (42.23%) > slag plus reed (36.19%) > small pebbles plus reed (33.49%) > centimeter stones plus cattail (21.14%) ; 30.29%-88.43%(average:50.99%) of CODcr, 21.80-74.75%(average:41.04%) of TN, 22.33%-83.47%(average:59.00%) of NH3-N and 16.54%-63.75%(average:31.75%) of TP could be removed through the free water system artificial "wetland; 6.05t/a, 0.14t/a, 0.02t/a, 1.01t/a 0.12t/a of N and 0.24t/a, 0.028t/a, 0.003t/a, 0.14t/a & 0.015t/a of P could be removed by the absorbing action of the system-depended plants such as water celery, cattail, reed, ling and lotus. The concentration of SS, BOD5, CODcr, TN and TP in the water treated by the constructed wetland system is 0.8-10mg/l, 4.1-24.5mg/l, 0.9-10.4mg/l & 0.2-0.98mg/l and the rate for the acceptance standard towards the project is up to 100%, 100%, 100%, 90.91 % and 72.73%.Conclusion: within the constructed wetland system, there are very strong inter-help and parataxis among the unit beds because the good pre-treatment of the former units lets the following nits able to make full use of their treatment functions. At the same time, this system has a high wastewater purification ability and a...