Nguyễn Văn Hòa * , Trương Chí Linh , Nguyễn Thị Hồng Vân , Nguyễn Thị Ngọc Anh , Phạm Thị Tuyết Ngân Đặng Kim Thanh

* Tác giả liên hệ (nvhoa@ctu.edu.vn)

Abstract

This study aimed to determine the suitable salinity for the development and formation of biofloc in fertilized ponds. The experiment was conducted at four different salinities (35, 60, 80 and 100 ppt) with 3 replicates per treatment and lasted for 21 days. Earthen ponds with area of 150 m2, water column of 30 cm were fertilized with chicken manure together tapioca to maintain the C:N ratio of ? 10. Results showed that the environmental factors (temperature, dissolved oxygen, pH) were suitable for the formation and development of biofloc. The C:N ratio ranges from 5 to 9. The TOC content at 35 ppt (20.21 to 50.5 mg/L) was less than at higher salinity (40 to 74.89 mg/L). The mean value of TSS and VSS were 20 to 670 mg/L and 7 to 126.6 mg/L, respectively and there was no significant difference among the treatments at day 18 and 21 (p>0.05). Total bacteria counts reached highest number at day 15 (4.1 log CFU/ml), the maximum volume of biofloc ranged from 0.4 to 0.5 ml and no significant difference among treatments (p>0.05). Vibrio, Bacillus, Nitrosomonas and Nitrobacter were found in all salinities, in which Bacillus presented with highest proportion. The ratio of un-known bacteria at salinity ? 60 ppt were very high (63-100%). At high salinity (80-100 ppt), floc size was smaller (32.5 - 61.5 àm wide; 61.3 - 97.9 àm long) than at low salinity (52,3 - 71.0 àm wide; 76.7 - 105.3 àm long). Proximate compositions analysis showed the low proportions of protein (8.5 to 17.4%) and lipid (0.65 to 1.08%), whereas ash content was very high (67.1 to 86.4%).
Keywords: Biofloc, salinity, fertilized pond, C:N ratio, proximate composition

Tóm tắt

Nghiên cứu này nhằm xác định độ mặn thích hợp cho sự phát triển và hình thành biofloc trong ao bón phân. Thí nghiệm gồm 4 nghiệm thức độ mặn (35, 60, 80 và 100 ppt) và được lặp lại 3 lần, thời gian thí nghiệm là 21 ngày. Ao thí nghiệm có diện tích 150 m2 với mực nước 30 cm và sử dụng phân gà + bột khoai mì để duy trì tỉ lệ C:N ?10. Kết quả thí nghiệm cho thấy các chỉ tiêu môi trường (nhiệt độ, oxy hòa tan, pH) nằm trong khoảng thích hợp cho sự hình thành và phát triển của biofloc. Tỷ lệ C:N dao động từ 5-9. Hàm lượng TOC thấp nhất ở 35 ppt (20,21-50,5 mg/L) và ở các độ mặn cao từ 40-74,89 mg/L. Hàm lượng TSS và VSS từ 20-670 mg/L và 7-126,6 mg/L và không có sự khác biệt giữa các độ mặn ở ngày 18 và 21 (P>0,05). Mật độ vi khuẩn tổng đạt cao nhất vào ngày 15 (4,1 log CFU/ml)), thể tích biofloc cao nhất là 0,4-0,5 ml và không có sự khác biệt giữa các độ mặn (P>0,05). Có 4 nhóm vi khuẩn được phát hiện là Vibrio, Baccillus, Nitrosomonas và Nitrobacter, trong đó nhóm Bacillus luôn chiếm tỷ lệ cao ở tất cả các độ mặn. Tỉ lệ vi khuẩn chưa định danh ở độ mặn ?60 ppt chiếm rất cao (63-100%). ở độ mặn cao (80-100 ppt) kích thuớc hạt biofloc nhỏ hơn (rộng: 32,5-61,5 àm và dài: 61,3-97,9 àm) so với ở độ mặn thấp (rộng: 52,3-71,0 àm và dài: 76,7-105,3 àm). Phân tích thành phần dinh dưỡng của biofloc cho thấy tỷ lệ của protein (8,5-17,4%) và lipid (0,65-1,08%) đều thấp, trong khi đó, hàm lượng tro rất cao (67,1-86,4%).
Từ khóa: biofloc, độ mặn, ao bón phân, tỉ lệ C:N, thành phần sinh hóa

Article Details

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