BOD removal in the anaerobic pond was a linear function of BOD loading and up to a loading of 2,000 pounds BOD per acre per day, 80%. A portion of the unseparated algal pond effluent was recycled to the anaerobic pond providing organic nitrogen, phosphorus and "seed" for microbial transformations. Loadings above 1,000 pounds BOD per acre per day are generally not permitted due to wind production and high effluent BOD.
With mechanical surface aeration at about 300 lbs O2 per day, a 14 ft deep, one acre anaerobic pond can be loaded at a rate of 1000 lbs final BOD per acre per day without excessive odor. Because of nitrogen losses, which have been found to be significant in the anaerobic pond, nitrogen must be added after passing the liquid through the anaerobic pond. Anaerobic pond loads should not exceed 1,000 lbs per acre per day, and aeration should be used on the surface of the anaerobic pond to the extent necessary to prevent odors.
RECOMMENDATIONS
INTRODUCTION
The majority of the removals of BOD, COD, nitrogen and other items occurred in the anaerobic pond; while the facultative and aerobic ponds only contributed slightly to the total purification and were therefore apparently underloaded. Because the system was designed to work, algae had to play a very important role in that they had to provide the oxygen removed in the aerobic pond and in the surface layers of the facultative pond. The availability of photosynthetic oxygen would have allowed a degree of BOD removal that was not possible in the absence of oxygen.
A further review of the results from the first period revealed several important pieces of information that were missing from the research and that needed to be obtained in these studies if full utilization of the system was to be achieved in practice. It was also considered important to determine the independent role of the facultative pond in the system and the independent role of the algal pond. Since the results obtained in the first research period indicated that a satisfactory performance of the facultative-aerobic phases is essential for the efficient functioning of the anaerobic-facultative-aerobic complex as a whole, the primary objective of the proposed research was to determine the effectiveness of the system with either the facultative or the aerobic ponds working in series with the primary or anaerobic pond.
Experience with other studies of natural aeration as well as the one obtained in the first study period without mechanical. Studies made in the first research period showed that it is high in carbon and BOD, that the 5-day BOD is about 67 percent of the COD, which indicates a relatively high biodegradability of the nutrients.
EXPERIMENTAL
Details of the weir construction designed to provide steady flow in the kelp pond are shown in Figure 3. When factory waste became available during the fall campaign of 1967, the drying and reconstruction of the kelp pond was not yet complete. Therefore, the anaerobic algae pond and facultative system were operated for the remainder of the 1967 fall campaign.
The contents of this bottle were labeled "influent" and analyzed daily as typical of the influent to the anaerobic pond. During the operation of the algae pool, there was an overflow into the effluent water collector and into the recirculation collector. During the course of the studies, several 24-hour studies were conducted to obtain information on the daily rates of oxidation and photosynthesis in the ponds.
This short circuit is estimated to have reduced the portion of the algae that was washed. This rate was chosen based on the theory that it would force more of the BOD load to be transported through the anaerobic pond and into the photosynthetic or algal pond.
RESULTS
Because of the high removals in the anaerobic pond, loadings to the facultative pond were always less than 180 pounds per day. The magnitude of decrease in BOD in the algae pond was from 30 to 126 mg per litre. Considerable photosynthetic activity also occurred in the anaerobic pond, as evidenced by the algae concentration of the pond.
Figure 16 shows a graph of the monthly average suspended ash in the influent and two ponds. Thus, in the algal pond and in the anaerobic pond, a smaller amount of dissolved ash was associated with higher specific conductance. Algae and sulfides occurred in the anaerobic pond and the light absorption was due to both.
In Figure 22, monthly average sulfate reduction is plotted as a function of monthly average temperature in the anaerobic pond. Some concentrations in the anaerobic pond were found to be as high as 6 mg per liter during August. Purple sulfur bacteria were found in the algal pond at the times when they were present in the anaerobic pond.
In the case of the anaerobic pond, in one sample an odor product of 24 was accompanied by a sulfide concentration of 0.1 mg per liter. The monthly average values for unfiltered COD in the influent, the anaerobic pond and algae pond are depicted in figure 28. In the case of the algae pond, the COD was initially 95% in the filterable form; while through the.
Apparently they could not survive in the generally anaerobic environment of the anaerobic pond. The enrichments were added to provide approximately 5 mg per liter of the fertilizer chemical in the final solution. Under the hottest temperatures encountered in the study, 250 ft3 of gas per acre per day was released from the bottom of the anaerobic pond.
A significant fraction of this CO2 was undoubtedly absorbed into the alkalinity of the water in the anaerobic pond.
GLOSSARY
APPENDICES
G-2 Daily amount of packed algae cells G-3 Number and/or occurrence of water flea G-A Number and/or occurrence of ringworms. Anaerobic pond gas emissions as measured by Bronson1 collector and wet water meter (litres/day). H-2 September Anaerobic pond H-3 October Anaerobic pond H-4 November Anaerobic pond H-5 December Anaerobic pond H-6 August August algae pond.
