Experimental studies were undertaken to examine the flow in long vertical conduits with particular reference to the design of storm water drop shafts. A distinguishing characteristic of such flow is the potential cavitation regime. Its existence depends upon the design of the structure. The cavitation regime will develop when the conduit is sufficiently long and the head sufficiently large. It can also be generated at a lower head if a control valve is installed in the supply line so that the net head can be negative. If a small amount of air is introduced into the system, the cavitation region is eliminated, the pressure gradient is more uniform, and the flow consists of a uniform mixture of air and water.

The water budget for the city of Laramie, Wyoming, was calculated for the years 1966-1970 in order to supplement studies of the city's sewage lagoons and to estimate the effects of municipal use on the Laramie River. Usage during the summer months (April-September) varied directly with temperature and inversely with rainfall, with an average of 235 gpcd. The river furnished approximately 1/3 of the annual supply, and more than 1/2 of the summer supply. On an annual basis, however the city returned more water to the river than it withdrew.

The introduction of sulfite waste liquors into streams often leads to the development of unsightly masses of biological slime dominated by Sphaerotilus. One approach for controlling the development of Sphaerotilus in streams receiving pulp mill wastes has been to employ biological methods for treating wastes before release into a receiving stream. The study evaluates the slime growth potential of pulp mill wastes treated by various methods of biodegradation. Wastes were tested both before and after secondary treatment in order to determine the type of biodegradable material present in the influent, determine the extent of fermentation during treatment, and the amount of biodegraded fermentable compounds discharged in the effluent. These studies were carried out in an effort to define total carbon, readily fermentable carbon, and to design a reasonably accurate and sensitive method for predicting adequate water quality presently measured by BOD.

A pilot scale field investigation of the effects of supplemental aeration on waste stabilization lagoons was conducted at Laramie, Wyoming, a low temperature, high altitude area. Both batch and complete mixed experiments were conducted using constant air flows. Loading rates, both hydraulic and process, were varied. The supplemental aeration provided both aeration and mixing, thereby increasing metabolic rates. BOD reductions varied from 72 to 85% under three different loadings, at temperatures of less than 12°C. No settleable solids were found in the effluent from the aerated system. Series operation was demonstrated to have the advantages of damping variations in quality parameters, providing for shock loading, and reducing coliform counts to minimum levels.

Bench scale batch experiments were performed on sludges obtained from line neutralization of coal mine drainage in an attempt to alleviate present problems in sludge handling and disposal. Tests were of an exploratory nature and did not afford sufficient data for cost analyses. Ferro Magnetic sludge densification, filter aids, coagulant aids, heating, freeze drying, and coprecipitation of calcium carbonate through addition of CO₂ were tested. Of these, freeze drying, CO₂ addition, and ferro magnetic treatment were shown to be feasible alternatives to present disposal methods. Each of these methods resulted in settled sludge volume reduction of approximately 90% and increases in sludge solids contents of from 0.5 to about 5% after 30 min. settling periods. The ferro magnetic process has the advantages of possible recovery of a useful product, and elimination of costly settling lagoons, but is very sensitive to aluminum and requires a considerable amount of heat. Sludge freezing is the simplest conceptual approach and is apparently effective for any lime produced sludge. The CO₂ addition method offers the possibility of partial recovery and recycling of both CaO and CO₂ through sludge calcination.

Studies were undertaken on a small scale to determine the effect liquid waste artificial iron-rich acid brines had on municipal sewage treatment processes. The brines were devised to simulate concentrates from treatment of acid mine drainage. At very high concentrations, the brines neutralized with lime give virtually complete removal of phosphate from primary effluent, activated sludge effluent, or anaerobic sludge digester decantate. The cost of the iron-rich acid brine produced from acid mine drainage by the reverse osmosis membrane treatment is estimated. Costs of transportation by rail, truck, and pipeline are also shown.

The status of the National Irrigation Return Flow Research and Development Program is presented. Current research projects and future program development are discussed. The report represents the position of the Environmental Protection Agency (EPA) with regard to the development of effective controls on the quality of irrigation return flows. Program goals and milestones are outlined. A number of potential control measures are discussed. Improvements in the water delivery system, on-the-farm water management, and the water removal system are considered with respect to improving the quality of irrigation return flows and decreasing the degradation of receiving waters. Research and investigations are needed to evaluate the effectiveness of potential control measures. Demonstrations and educational activities will be required to overcome institutional, political, and legal constraints to water management reform.